diff options
Diffstat (limited to 'kernel/arch/x86/lguest')
| -rw-r--r-- | kernel/arch/x86/lguest/Kconfig | 14 | ||||
| -rw-r--r-- | kernel/arch/x86/lguest/Makefile | 2 | ||||
| -rw-r--r-- | kernel/arch/x86/lguest/boot.c | 1592 | ||||
| -rw-r--r-- | kernel/arch/x86/lguest/head_32.S | 192 |
4 files changed, 1800 insertions, 0 deletions
diff --git a/kernel/arch/x86/lguest/Kconfig b/kernel/arch/x86/lguest/Kconfig new file mode 100644 index 000000000..08f41caad --- /dev/null +++ b/kernel/arch/x86/lguest/Kconfig @@ -0,0 +1,14 @@ +config LGUEST_GUEST + bool "Lguest guest support" + depends on X86_32 && PARAVIRT && PCI + select TTY + select VIRTUALIZATION + select VIRTIO + select VIRTIO_CONSOLE + help + Lguest is a tiny in-kernel hypervisor. Selecting this will + allow your kernel to boot under lguest. This option will increase + your kernel size by about 10k. If in doubt, say N. + + If you say Y here, make sure you say Y (or M) to the virtio block + and net drivers which lguest needs. diff --git a/kernel/arch/x86/lguest/Makefile b/kernel/arch/x86/lguest/Makefile new file mode 100644 index 000000000..8f38d577a --- /dev/null +++ b/kernel/arch/x86/lguest/Makefile @@ -0,0 +1,2 @@ +obj-y := head_32.o boot.o +CFLAGS_boot.o := $(call cc-option, -fno-stack-protector) diff --git a/kernel/arch/x86/lguest/boot.c b/kernel/arch/x86/lguest/boot.c new file mode 100644 index 000000000..8f9a133cc --- /dev/null +++ b/kernel/arch/x86/lguest/boot.c @@ -0,0 +1,1592 @@ +/*P:010 + * A hypervisor allows multiple Operating Systems to run on a single machine. + * To quote David Wheeler: "Any problem in computer science can be solved with + * another layer of indirection." + * + * We keep things simple in two ways. First, we start with a normal Linux + * kernel and insert a module (lg.ko) which allows us to run other Linux + * kernels the same way we'd run processes. We call the first kernel the Host, + * and the others the Guests. The program which sets up and configures Guests + * (such as the example in tools/lguest/lguest.c) is called the Launcher. + * + * Secondly, we only run specially modified Guests, not normal kernels: setting + * CONFIG_LGUEST_GUEST to "y" compiles this file into the kernel so it knows + * how to be a Guest at boot time. This means that you can use the same kernel + * you boot normally (ie. as a Host) as a Guest. + * + * These Guests know that they cannot do privileged operations, such as disable + * interrupts, and that they have to ask the Host to do such things explicitly. + * This file consists of all the replacements for such low-level native + * hardware operations: these special Guest versions call the Host. + * + * So how does the kernel know it's a Guest? We'll see that later, but let's + * just say that we end up here where we replace the native functions various + * "paravirt" structures with our Guest versions, then boot like normal. +:*/ + +/* + * Copyright (C) 2006, Rusty Russell <rusty@rustcorp.com.au> IBM Corporation. + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, but + * WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or + * NON INFRINGEMENT. See the GNU General Public License for more + * details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. + */ +#include <linux/kernel.h> +#include <linux/start_kernel.h> +#include <linux/string.h> +#include <linux/console.h> +#include <linux/screen_info.h> +#include <linux/irq.h> +#include <linux/interrupt.h> +#include <linux/clocksource.h> +#include <linux/clockchips.h> +#include <linux/lguest.h> +#include <linux/lguest_launcher.h> +#include <linux/virtio_console.h> +#include <linux/pm.h> +#include <linux/export.h> +#include <linux/pci.h> +#include <linux/virtio_pci.h> +#include <asm/acpi.h> +#include <asm/apic.h> +#include <asm/lguest.h> +#include <asm/paravirt.h> +#include <asm/param.h> +#include <asm/page.h> +#include <asm/pgtable.h> +#include <asm/desc.h> +#include <asm/setup.h> +#include <asm/e820.h> +#include <asm/mce.h> +#include <asm/io.h> +#include <asm/i387.h> +#include <asm/stackprotector.h> +#include <asm/reboot.h> /* for struct machine_ops */ +#include <asm/kvm_para.h> +#include <asm/pci_x86.h> +#include <asm/pci-direct.h> + +/*G:010 + * Welcome to the Guest! + * + * The Guest in our tale is a simple creature: identical to the Host but + * behaving in simplified but equivalent ways. In particular, the Guest is the + * same kernel as the Host (or at least, built from the same source code). +:*/ + +struct lguest_data lguest_data = { + .hcall_status = { [0 ... LHCALL_RING_SIZE-1] = 0xFF }, + .noirq_iret = (u32)lguest_noirq_iret, + .kernel_address = PAGE_OFFSET, + .blocked_interrupts = { 1 }, /* Block timer interrupts */ + .syscall_vec = SYSCALL_VECTOR, +}; + +/*G:037 + * async_hcall() is pretty simple: I'm quite proud of it really. We have a + * ring buffer of stored hypercalls which the Host will run though next time we + * do a normal hypercall. Each entry in the ring has 5 slots for the hypercall + * arguments, and a "hcall_status" word which is 0 if the call is ready to go, + * and 255 once the Host has finished with it. + * + * If we come around to a slot which hasn't been finished, then the table is + * full and we just make the hypercall directly. This has the nice side + * effect of causing the Host to run all the stored calls in the ring buffer + * which empties it for next time! + */ +static void async_hcall(unsigned long call, unsigned long arg1, + unsigned long arg2, unsigned long arg3, + unsigned long arg4) +{ + /* Note: This code assumes we're uniprocessor. */ + static unsigned int next_call; + unsigned long flags; + + /* + * Disable interrupts if not already disabled: we don't want an + * interrupt handler making a hypercall while we're already doing + * one! + */ + local_irq_save(flags); + if (lguest_data.hcall_status[next_call] != 0xFF) { + /* Table full, so do normal hcall which will flush table. */ + hcall(call, arg1, arg2, arg3, arg4); + } else { + lguest_data.hcalls[next_call].arg0 = call; + lguest_data.hcalls[next_call].arg1 = arg1; + lguest_data.hcalls[next_call].arg2 = arg2; + lguest_data.hcalls[next_call].arg3 = arg3; + lguest_data.hcalls[next_call].arg4 = arg4; + /* Arguments must all be written before we mark it to go */ + wmb(); + lguest_data.hcall_status[next_call] = 0; + if (++next_call == LHCALL_RING_SIZE) + next_call = 0; + } + local_irq_restore(flags); +} + +/*G:035 + * Notice the lazy_hcall() above, rather than hcall(). This is our first real + * optimization trick! + * + * When lazy_mode is set, it means we're allowed to defer all hypercalls and do + * them as a batch when lazy_mode is eventually turned off. Because hypercalls + * are reasonably expensive, batching them up makes sense. For example, a + * large munmap might update dozens of page table entries: that code calls + * paravirt_enter_lazy_mmu(), does the dozen updates, then calls + * lguest_leave_lazy_mode(). + * + * So, when we're in lazy mode, we call async_hcall() to store the call for + * future processing: + */ +static void lazy_hcall1(unsigned long call, unsigned long arg1) +{ + if (paravirt_get_lazy_mode() == PARAVIRT_LAZY_NONE) + hcall(call, arg1, 0, 0, 0); + else + async_hcall(call, arg1, 0, 0, 0); +} + +/* You can imagine what lazy_hcall2, 3 and 4 look like. :*/ +static void lazy_hcall2(unsigned long call, + unsigned long arg1, + unsigned long arg2) +{ + if (paravirt_get_lazy_mode() == PARAVIRT_LAZY_NONE) + hcall(call, arg1, arg2, 0, 0); + else + async_hcall(call, arg1, arg2, 0, 0); +} + +static void lazy_hcall3(unsigned long call, + unsigned long arg1, + unsigned long arg2, + unsigned long arg3) +{ + if (paravirt_get_lazy_mode() == PARAVIRT_LAZY_NONE) + hcall(call, arg1, arg2, arg3, 0); + else + async_hcall(call, arg1, arg2, arg3, 0); +} + +#ifdef CONFIG_X86_PAE +static void lazy_hcall4(unsigned long call, + unsigned long arg1, + unsigned long arg2, + unsigned long arg3, + unsigned long arg4) +{ + if (paravirt_get_lazy_mode() == PARAVIRT_LAZY_NONE) + hcall(call, arg1, arg2, arg3, arg4); + else + async_hcall(call, arg1, arg2, arg3, arg4); +} +#endif + +/*G:036 + * When lazy mode is turned off, we issue the do-nothing hypercall to + * flush any stored calls, and call the generic helper to reset the + * per-cpu lazy mode variable. + */ +static void lguest_leave_lazy_mmu_mode(void) +{ + hcall(LHCALL_FLUSH_ASYNC, 0, 0, 0, 0); + paravirt_leave_lazy_mmu(); +} + +/* + * We also catch the end of context switch; we enter lazy mode for much of + * that too, so again we need to flush here. + * + * (Technically, this is lazy CPU mode, and normally we're in lazy MMU + * mode, but unlike Xen, lguest doesn't care about the difference). + */ +static void lguest_end_context_switch(struct task_struct *next) +{ + hcall(LHCALL_FLUSH_ASYNC, 0, 0, 0, 0); + paravirt_end_context_switch(next); +} + +/*G:032 + * After that diversion we return to our first native-instruction + * replacements: four functions for interrupt control. + * + * The simplest way of implementing these would be to have "turn interrupts + * off" and "turn interrupts on" hypercalls. Unfortunately, this is too slow: + * these are by far the most commonly called functions of those we override. + * + * So instead we keep an "irq_enabled" field inside our "struct lguest_data", + * which the Guest can update with a single instruction. The Host knows to + * check there before it tries to deliver an interrupt. + */ + +/* + * save_flags() is expected to return the processor state (ie. "flags"). The + * flags word contains all kind of stuff, but in practice Linux only cares + * about the interrupt flag. Our "save_flags()" just returns that. + */ +asmlinkage __visible unsigned long lguest_save_fl(void) +{ + return lguest_data.irq_enabled; +} + +/* Interrupts go off... */ +asmlinkage __visible void lguest_irq_disable(void) +{ + lguest_data.irq_enabled = 0; +} + +/* + * Let's pause a moment. Remember how I said these are called so often? + * Jeremy Fitzhardinge optimized them so hard early in 2009 that he had to + * break some rules. In particular, these functions are assumed to save their + * own registers if they need to: normal C functions assume they can trash the + * eax register. To use normal C functions, we use + * PV_CALLEE_SAVE_REGS_THUNK(), which pushes %eax onto the stack, calls the + * C function, then restores it. + */ +PV_CALLEE_SAVE_REGS_THUNK(lguest_save_fl); +PV_CALLEE_SAVE_REGS_THUNK(lguest_irq_disable); +/*:*/ + +/* These are in head_32.S */ +extern void lg_irq_enable(void); +extern void lg_restore_fl(unsigned long flags); + +/*M:003 + * We could be more efficient in our checking of outstanding interrupts, rather + * than using a branch. One way would be to put the "irq_enabled" field in a + * page by itself, and have the Host write-protect it when an interrupt comes + * in when irqs are disabled. There will then be a page fault as soon as + * interrupts are re-enabled. + * + * A better method is to implement soft interrupt disable generally for x86: + * instead of disabling interrupts, we set a flag. If an interrupt does come + * in, we then disable them for real. This is uncommon, so we could simply use + * a hypercall for interrupt control and not worry about efficiency. +:*/ + +/*G:034 + * The Interrupt Descriptor Table (IDT). + * + * The IDT tells the processor what to do when an interrupt comes in. Each + * entry in the table is a 64-bit descriptor: this holds the privilege level, + * address of the handler, and... well, who cares? The Guest just asks the + * Host to make the change anyway, because the Host controls the real IDT. + */ +static void lguest_write_idt_entry(gate_desc *dt, + int entrynum, const gate_desc *g) +{ + /* + * The gate_desc structure is 8 bytes long: we hand it to the Host in + * two 32-bit chunks. The whole 32-bit kernel used to hand descriptors + * around like this; typesafety wasn't a big concern in Linux's early + * years. + */ + u32 *desc = (u32 *)g; + /* Keep the local copy up to date. */ + native_write_idt_entry(dt, entrynum, g); + /* Tell Host about this new entry. */ + hcall(LHCALL_LOAD_IDT_ENTRY, entrynum, desc[0], desc[1], 0); +} + +/* + * Changing to a different IDT is very rare: we keep the IDT up-to-date every + * time it is written, so we can simply loop through all entries and tell the + * Host about them. + */ +static void lguest_load_idt(const struct desc_ptr *desc) +{ + unsigned int i; + struct desc_struct *idt = (void *)desc->address; + + for (i = 0; i < (desc->size+1)/8; i++) + hcall(LHCALL_LOAD_IDT_ENTRY, i, idt[i].a, idt[i].b, 0); +} + +/* + * The Global Descriptor Table. + * + * The Intel architecture defines another table, called the Global Descriptor + * Table (GDT). You tell the CPU where it is (and its size) using the "lgdt" + * instruction, and then several other instructions refer to entries in the + * table. There are three entries which the Switcher needs, so the Host simply + * controls the entire thing and the Guest asks it to make changes using the + * LOAD_GDT hypercall. + * + * This is the exactly like the IDT code. + */ +static void lguest_load_gdt(const struct desc_ptr *desc) +{ + unsigned int i; + struct desc_struct *gdt = (void *)desc->address; + + for (i = 0; i < (desc->size+1)/8; i++) + hcall(LHCALL_LOAD_GDT_ENTRY, i, gdt[i].a, gdt[i].b, 0); +} + +/* + * For a single GDT entry which changes, we simply change our copy and + * then tell the host about it. + */ +static void lguest_write_gdt_entry(struct desc_struct *dt, int entrynum, + const void *desc, int type) +{ + native_write_gdt_entry(dt, entrynum, desc, type); + /* Tell Host about this new entry. */ + hcall(LHCALL_LOAD_GDT_ENTRY, entrynum, + dt[entrynum].a, dt[entrynum].b, 0); +} + +/* + * There are three "thread local storage" GDT entries which change + * on every context switch (these three entries are how glibc implements + * __thread variables). As an optimization, we have a hypercall + * specifically for this case. + * + * Wouldn't it be nicer to have a general LOAD_GDT_ENTRIES hypercall + * which took a range of entries? + */ +static void lguest_load_tls(struct thread_struct *t, unsigned int cpu) +{ + /* + * There's one problem which normal hardware doesn't have: the Host + * can't handle us removing entries we're currently using. So we clear + * the GS register here: if it's needed it'll be reloaded anyway. + */ + lazy_load_gs(0); + lazy_hcall2(LHCALL_LOAD_TLS, __pa(&t->tls_array), cpu); +} + +/*G:038 + * That's enough excitement for now, back to ploughing through each of the + * different pv_ops structures (we're about 1/3 of the way through). + * + * This is the Local Descriptor Table, another weird Intel thingy. Linux only + * uses this for some strange applications like Wine. We don't do anything + * here, so they'll get an informative and friendly Segmentation Fault. + */ +static void lguest_set_ldt(const void *addr, unsigned entries) +{ +} + +/* + * This loads a GDT entry into the "Task Register": that entry points to a + * structure called the Task State Segment. Some comments scattered though the + * kernel code indicate that this used for task switching in ages past, along + * with blood sacrifice and astrology. + * + * Now there's nothing interesting in here that we don't get told elsewhere. + * But the native version uses the "ltr" instruction, which makes the Host + * complain to the Guest about a Segmentation Fault and it'll oops. So we + * override the native version with a do-nothing version. + */ +static void lguest_load_tr_desc(void) +{ +} + +/* + * The "cpuid" instruction is a way of querying both the CPU identity + * (manufacturer, model, etc) and its features. It was introduced before the + * Pentium in 1993 and keeps getting extended by both Intel, AMD and others. + * As you might imagine, after a decade and a half this treatment, it is now a + * giant ball of hair. Its entry in the current Intel manual runs to 28 pages. + * + * This instruction even it has its own Wikipedia entry. The Wikipedia entry + * has been translated into 6 languages. I am not making this up! + * + * We could get funky here and identify ourselves as "GenuineLguest", but + * instead we just use the real "cpuid" instruction. Then I pretty much turned + * off feature bits until the Guest booted. (Don't say that: you'll damage + * lguest sales!) Shut up, inner voice! (Hey, just pointing out that this is + * hardly future proof.) No one's listening! They don't like you anyway, + * parenthetic weirdo! + * + * Replacing the cpuid so we can turn features off is great for the kernel, but + * anyone (including userspace) can just use the raw "cpuid" instruction and + * the Host won't even notice since it isn't privileged. So we try not to get + * too worked up about it. + */ +static void lguest_cpuid(unsigned int *ax, unsigned int *bx, + unsigned int *cx, unsigned int *dx) +{ + int function = *ax; + + native_cpuid(ax, bx, cx, dx); + switch (function) { + /* + * CPUID 0 gives the highest legal CPUID number (and the ID string). + * We futureproof our code a little by sticking to known CPUID values. + */ + case 0: + if (*ax > 5) + *ax = 5; + break; + + /* + * CPUID 1 is a basic feature request. + * + * CX: we only allow kernel to see SSE3, CMPXCHG16B and SSSE3 + * DX: SSE, SSE2, FXSR, MMX, CMOV, CMPXCHG8B, TSC, FPU and PAE. + */ + case 1: + *cx &= 0x00002201; + *dx &= 0x07808151; + /* + * The Host can do a nice optimization if it knows that the + * kernel mappings (addresses above 0xC0000000 or whatever + * PAGE_OFFSET is set to) haven't changed. But Linux calls + * flush_tlb_user() for both user and kernel mappings unless + * the Page Global Enable (PGE) feature bit is set. + */ + *dx |= 0x00002000; + /* + * We also lie, and say we're family id 5. 6 or greater + * leads to a rdmsr in early_init_intel which we can't handle. + * Family ID is returned as bits 8-12 in ax. + */ + *ax &= 0xFFFFF0FF; + *ax |= 0x00000500; + break; + + /* + * This is used to detect if we're running under KVM. We might be, + * but that's a Host matter, not us. So say we're not. + */ + case KVM_CPUID_SIGNATURE: + *bx = *cx = *dx = 0; + break; + + /* + * 0x80000000 returns the highest Extended Function, so we futureproof + * like we do above by limiting it to known fields. + */ + case 0x80000000: + if (*ax > 0x80000008) + *ax = 0x80000008; + break; + + /* + * PAE systems can mark pages as non-executable. Linux calls this the + * NX bit. Intel calls it XD (eXecute Disable), AMD EVP (Enhanced + * Virus Protection). We just switch it off here, since we don't + * support it. + */ + case 0x80000001: + *dx &= ~(1 << 20); + break; + } +} + +/* + * Intel has four control registers, imaginatively named cr0, cr2, cr3 and cr4. + * I assume there's a cr1, but it hasn't bothered us yet, so we'll not bother + * it. The Host needs to know when the Guest wants to change them, so we have + * a whole series of functions like read_cr0() and write_cr0(). + * + * We start with cr0. cr0 allows you to turn on and off all kinds of basic + * features, but Linux only really cares about one: the horrifically-named Task + * Switched (TS) bit at bit 3 (ie. 8) + * + * What does the TS bit do? Well, it causes the CPU to trap (interrupt 7) if + * the floating point unit is used. Which allows us to restore FPU state + * lazily after a task switch, and Linux uses that gratefully, but wouldn't a + * name like "FPUTRAP bit" be a little less cryptic? + * + * We store cr0 locally because the Host never changes it. The Guest sometimes + * wants to read it and we'd prefer not to bother the Host unnecessarily. + */ +static unsigned long current_cr0; +static void lguest_write_cr0(unsigned long val) +{ + lazy_hcall1(LHCALL_TS, val & X86_CR0_TS); + current_cr0 = val; +} + +static unsigned long lguest_read_cr0(void) +{ + return current_cr0; +} + +/* + * Intel provided a special instruction to clear the TS bit for people too cool + * to use write_cr0() to do it. This "clts" instruction is faster, because all + * the vowels have been optimized out. + */ +static void lguest_clts(void) +{ + lazy_hcall1(LHCALL_TS, 0); + current_cr0 &= ~X86_CR0_TS; +} + +/* + * cr2 is the virtual address of the last page fault, which the Guest only ever + * reads. The Host kindly writes this into our "struct lguest_data", so we + * just read it out of there. + */ +static unsigned long lguest_read_cr2(void) +{ + return lguest_data.cr2; +} + +/* See lguest_set_pte() below. */ +static bool cr3_changed = false; +static unsigned long current_cr3; + +/* + * cr3 is the current toplevel pagetable page: the principle is the same as + * cr0. Keep a local copy, and tell the Host when it changes. + */ +static void lguest_write_cr3(unsigned long cr3) +{ + lazy_hcall1(LHCALL_NEW_PGTABLE, cr3); + current_cr3 = cr3; + + /* These two page tables are simple, linear, and used during boot */ + if (cr3 != __pa_symbol(swapper_pg_dir) && + cr3 != __pa_symbol(initial_page_table)) + cr3_changed = true; +} + +static unsigned long lguest_read_cr3(void) +{ + return current_cr3; +} + +/* cr4 is used to enable and disable PGE, but we don't care. */ +static unsigned long lguest_read_cr4(void) +{ + return 0; +} + +static void lguest_write_cr4(unsigned long val) +{ +} + +/* + * Page Table Handling. + * + * Now would be a good time to take a rest and grab a coffee or similarly + * relaxing stimulant. The easy parts are behind us, and the trek gradually + * winds uphill from here. + * + * Quick refresher: memory is divided into "pages" of 4096 bytes each. The CPU + * maps virtual addresses to physical addresses using "page tables". We could + * use one huge index of 1 million entries: each address is 4 bytes, so that's + * 1024 pages just to hold the page tables. But since most virtual addresses + * are unused, we use a two level index which saves space. The cr3 register + * contains the physical address of the top level "page directory" page, which + * contains physical addresses of up to 1024 second-level pages. Each of these + * second level pages contains up to 1024 physical addresses of actual pages, + * or Page Table Entries (PTEs). + * + * Here's a diagram, where arrows indicate physical addresses: + * + * cr3 ---> +---------+ + * | --------->+---------+ + * | | | PADDR1 | + * Mid-level | | PADDR2 | + * (PMD) page | | | + * | | Lower-level | + * | | (PTE) page | + * | | | | + * .... .... + * + * So to convert a virtual address to a physical address, we look up the top + * level, which points us to the second level, which gives us the physical + * address of that page. If the top level entry was not present, or the second + * level entry was not present, then the virtual address is invalid (we + * say "the page was not mapped"). + * + * Put another way, a 32-bit virtual address is divided up like so: + * + * 1 1 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 + * |<---- 10 bits ---->|<---- 10 bits ---->|<------ 12 bits ------>| + * Index into top Index into second Offset within page + * page directory page pagetable page + * + * Now, unfortunately, this isn't the whole story: Intel added Physical Address + * Extension (PAE) to allow 32 bit systems to use 64GB of memory (ie. 36 bits). + * These are held in 64-bit page table entries, so we can now only fit 512 + * entries in a page, and the neat three-level tree breaks down. + * + * The result is a four level page table: + * + * cr3 --> [ 4 Upper ] + * [ Level ] + * [ Entries ] + * [(PUD Page)]---> +---------+ + * | --------->+---------+ + * | | | PADDR1 | + * Mid-level | | PADDR2 | + * (PMD) page | | | + * | | Lower-level | + * | | (PTE) page | + * | | | | + * .... .... + * + * + * And the virtual address is decoded as: + * + * 1 1 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 + * |<-2->|<--- 9 bits ---->|<---- 9 bits --->|<------ 12 bits ------>| + * Index into Index into mid Index into lower Offset within page + * top entries directory page pagetable page + * + * It's too hard to switch between these two formats at runtime, so Linux only + * supports one or the other depending on whether CONFIG_X86_PAE is set. Many + * distributions turn it on, and not just for people with silly amounts of + * memory: the larger PTE entries allow room for the NX bit, which lets the + * kernel disable execution of pages and increase security. + * + * This was a problem for lguest, which couldn't run on these distributions; + * then Matias Zabaljauregui figured it all out and implemented it, and only a + * handful of puppies were crushed in the process! + * + * Back to our point: the kernel spends a lot of time changing both the + * top-level page directory and lower-level pagetable pages. The Guest doesn't + * know physical addresses, so while it maintains these page tables exactly + * like normal, it also needs to keep the Host informed whenever it makes a + * change: the Host will create the real page tables based on the Guests'. + */ + +/* + * The Guest calls this after it has set a second-level entry (pte), ie. to map + * a page into a process' address space. We tell the Host the toplevel and + * address this corresponds to. The Guest uses one pagetable per process, so + * we need to tell the Host which one we're changing (mm->pgd). + */ +static void lguest_pte_update(struct mm_struct *mm, unsigned long addr, + pte_t *ptep) +{ +#ifdef CONFIG_X86_PAE + /* PAE needs to hand a 64 bit page table entry, so it uses two args. */ + lazy_hcall4(LHCALL_SET_PTE, __pa(mm->pgd), addr, + ptep->pte_low, ptep->pte_high); +#else + lazy_hcall3(LHCALL_SET_PTE, __pa(mm->pgd), addr, ptep->pte_low); +#endif +} + +/* This is the "set and update" combo-meal-deal version. */ +static void lguest_set_pte_at(struct mm_struct *mm, unsigned long addr, + pte_t *ptep, pte_t pteval) +{ + native_set_pte(ptep, pteval); + lguest_pte_update(mm, addr, ptep); +} + +/* + * The Guest calls lguest_set_pud to set a top-level entry and lguest_set_pmd + * to set a middle-level entry when PAE is activated. + * + * Again, we set the entry then tell the Host which page we changed, + * and the index of the entry we changed. + */ +#ifdef CONFIG_X86_PAE +static void lguest_set_pud(pud_t *pudp, pud_t pudval) +{ + native_set_pud(pudp, pudval); + + /* 32 bytes aligned pdpt address and the index. */ + lazy_hcall2(LHCALL_SET_PGD, __pa(pudp) & 0xFFFFFFE0, + (__pa(pudp) & 0x1F) / sizeof(pud_t)); +} + +static void lguest_set_pmd(pmd_t *pmdp, pmd_t pmdval) +{ + native_set_pmd(pmdp, pmdval); + lazy_hcall2(LHCALL_SET_PMD, __pa(pmdp) & PAGE_MASK, + (__pa(pmdp) & (PAGE_SIZE - 1)) / sizeof(pmd_t)); +} +#else + +/* The Guest calls lguest_set_pmd to set a top-level entry when !PAE. */ +static void lguest_set_pmd(pmd_t *pmdp, pmd_t pmdval) +{ + native_set_pmd(pmdp, pmdval); + lazy_hcall2(LHCALL_SET_PGD, __pa(pmdp) & PAGE_MASK, + (__pa(pmdp) & (PAGE_SIZE - 1)) / sizeof(pmd_t)); +} +#endif + +/* + * There are a couple of legacy places where the kernel sets a PTE, but we + * don't know the top level any more. This is useless for us, since we don't + * know which pagetable is changing or what address, so we just tell the Host + * to forget all of them. Fortunately, this is very rare. + * + * ... except in early boot when the kernel sets up the initial pagetables, + * which makes booting astonishingly slow: 48 seconds! So we don't even tell + * the Host anything changed until we've done the first real page table switch, + * which brings boot back to 4.3 seconds. + */ +static void lguest_set_pte(pte_t *ptep, pte_t pteval) +{ + native_set_pte(ptep, pteval); + if (cr3_changed) + lazy_hcall1(LHCALL_FLUSH_TLB, 1); +} + +#ifdef CONFIG_X86_PAE +/* + * With 64-bit PTE values, we need to be careful setting them: if we set 32 + * bits at a time, the hardware could see a weird half-set entry. These + * versions ensure we update all 64 bits at once. + */ +static void lguest_set_pte_atomic(pte_t *ptep, pte_t pte) +{ + native_set_pte_atomic(ptep, pte); + if (cr3_changed) + lazy_hcall1(LHCALL_FLUSH_TLB, 1); +} + +static void lguest_pte_clear(struct mm_struct *mm, unsigned long addr, + pte_t *ptep) +{ + native_pte_clear(mm, addr, ptep); + lguest_pte_update(mm, addr, ptep); +} + +static void lguest_pmd_clear(pmd_t *pmdp) +{ + lguest_set_pmd(pmdp, __pmd(0)); +} +#endif + +/* + * Unfortunately for Lguest, the pv_mmu_ops for page tables were based on + * native page table operations. On native hardware you can set a new page + * table entry whenever you want, but if you want to remove one you have to do + * a TLB flush (a TLB is a little cache of page table entries kept by the CPU). + * + * So the lguest_set_pte_at() and lguest_set_pmd() functions above are only + * called when a valid entry is written, not when it's removed (ie. marked not + * present). Instead, this is where we come when the Guest wants to remove a + * page table entry: we tell the Host to set that entry to 0 (ie. the present + * bit is zero). + */ +static void lguest_flush_tlb_single(unsigned long addr) +{ + /* Simply set it to zero: if it was not, it will fault back in. */ + lazy_hcall3(LHCALL_SET_PTE, current_cr3, addr, 0); +} + +/* + * This is what happens after the Guest has removed a large number of entries. + * This tells the Host that any of the page table entries for userspace might + * have changed, ie. virtual addresses below PAGE_OFFSET. + */ +static void lguest_flush_tlb_user(void) +{ + lazy_hcall1(LHCALL_FLUSH_TLB, 0); +} + +/* + * This is called when the kernel page tables have changed. That's not very + * common (unless the Guest is using highmem, which makes the Guest extremely + * slow), so it's worth separating this from the user flushing above. + */ +static void lguest_flush_tlb_kernel(void) +{ + lazy_hcall1(LHCALL_FLUSH_TLB, 1); +} + +/* + * The Unadvanced Programmable Interrupt Controller. + * + * This is an attempt to implement the simplest possible interrupt controller. + * I spent some time looking though routines like set_irq_chip_and_handler, + * set_irq_chip_and_handler_name, set_irq_chip_data and set_phasers_to_stun and + * I *think* this is as simple as it gets. + * + * We can tell the Host what interrupts we want blocked ready for using the + * lguest_data.interrupts bitmap, so disabling (aka "masking") them is as + * simple as setting a bit. We don't actually "ack" interrupts as such, we + * just mask and unmask them. I wonder if we should be cleverer? + */ +static void disable_lguest_irq(struct irq_data *data) +{ + set_bit(data->irq, lguest_data.blocked_interrupts); +} + +static void enable_lguest_irq(struct irq_data *data) +{ + clear_bit(data->irq, lguest_data.blocked_interrupts); +} + +/* This structure describes the lguest IRQ controller. */ +static struct irq_chip lguest_irq_controller = { + .name = "lguest", + .irq_mask = disable_lguest_irq, + .irq_mask_ack = disable_lguest_irq, + .irq_unmask = enable_lguest_irq, +}; + +static int lguest_enable_irq(struct pci_dev *dev) +{ + u8 line = 0; + + /* We literally use the PCI interrupt line as the irq number. */ + pci_read_config_byte(dev, PCI_INTERRUPT_LINE, &line); + irq_set_chip_and_handler_name(line, &lguest_irq_controller, + handle_level_irq, "level"); + dev->irq = line; + return 0; +} + +/* We don't do hotplug PCI, so this shouldn't be called. */ +static void lguest_disable_irq(struct pci_dev *dev) +{ + WARN_ON(1); +} + +/* + * This sets up the Interrupt Descriptor Table (IDT) entry for each hardware + * interrupt (except 128, which is used for system calls), and then tells the + * Linux infrastructure that each interrupt is controlled by our level-based + * lguest interrupt controller. + */ +static void __init lguest_init_IRQ(void) +{ + unsigned int i; + + for (i = FIRST_EXTERNAL_VECTOR; i < FIRST_SYSTEM_VECTOR; i++) { + /* Some systems map "vectors" to interrupts weirdly. Not us! */ + __this_cpu_write(vector_irq[i], i - FIRST_EXTERNAL_VECTOR); + if (i != SYSCALL_VECTOR) + set_intr_gate(i, irq_entries_start + + 8 * (i - FIRST_EXTERNAL_VECTOR)); + } + + /* + * This call is required to set up for 4k stacks, where we have + * separate stacks for hard and soft interrupts. + */ + irq_ctx_init(smp_processor_id()); +} + +/* + * Interrupt descriptors are allocated as-needed, but low-numbered ones are + * reserved by the generic x86 code. So we ignore irq_alloc_desc_at if it + * tells us the irq is already used: other errors (ie. ENOMEM) we take + * seriously. + */ +int lguest_setup_irq(unsigned int irq) +{ + int err; + + /* Returns -ve error or vector number. */ + err = irq_alloc_desc_at(irq, 0); + if (err < 0 && err != -EEXIST) + return err; + + irq_set_chip_and_handler_name(irq, &lguest_irq_controller, + handle_level_irq, "level"); + return 0; +} + +/* + * Time. + * + * It would be far better for everyone if the Guest had its own clock, but + * until then the Host gives us the time on every interrupt. + */ +static void lguest_get_wallclock(struct timespec *now) +{ + *now = lguest_data.time; +} + +/* + * The TSC is an Intel thing called the Time Stamp Counter. The Host tells us + * what speed it runs at, or 0 if it's unusable as a reliable clock source. + * This matches what we want here: if we return 0 from this function, the x86 + * TSC clock will give up and not register itself. + */ +static unsigned long lguest_tsc_khz(void) +{ + return lguest_data.tsc_khz; +} + +/* + * If we can't use the TSC, the kernel falls back to our lower-priority + * "lguest_clock", where we read the time value given to us by the Host. + */ +static cycle_t lguest_clock_read(struct clocksource *cs) +{ + unsigned long sec, nsec; + + /* + * Since the time is in two parts (seconds and nanoseconds), we risk + * reading it just as it's changing from 99 & 0.999999999 to 100 and 0, + * and getting 99 and 0. As Linux tends to come apart under the stress + * of time travel, we must be careful: + */ + do { + /* First we read the seconds part. */ + sec = lguest_data.time.tv_sec; + /* + * This read memory barrier tells the compiler and the CPU that + * this can't be reordered: we have to complete the above + * before going on. + */ + rmb(); + /* Now we read the nanoseconds part. */ + nsec = lguest_data.time.tv_nsec; + /* Make sure we've done that. */ + rmb(); + /* Now if the seconds part has changed, try again. */ + } while (unlikely(lguest_data.time.tv_sec != sec)); + + /* Our lguest clock is in real nanoseconds. */ + return sec*1000000000ULL + nsec; +} + +/* This is the fallback clocksource: lower priority than the TSC clocksource. */ +static struct clocksource lguest_clock = { + .name = "lguest", + .rating = 200, + .read = lguest_clock_read, + .mask = CLOCKSOURCE_MASK(64), + .flags = CLOCK_SOURCE_IS_CONTINUOUS, +}; + +/* + * We also need a "struct clock_event_device": Linux asks us to set it to go + * off some time in the future. Actually, James Morris figured all this out, I + * just applied the patch. + */ +static int lguest_clockevent_set_next_event(unsigned long delta, + struct clock_event_device *evt) +{ + /* FIXME: I don't think this can ever happen, but James tells me he had + * to put this code in. Maybe we should remove it now. Anyone? */ + if (delta < LG_CLOCK_MIN_DELTA) { + if (printk_ratelimit()) + printk(KERN_DEBUG "%s: small delta %lu ns\n", + __func__, delta); + return -ETIME; + } + + /* Please wake us this far in the future. */ + hcall(LHCALL_SET_CLOCKEVENT, delta, 0, 0, 0); + return 0; +} + +static void lguest_clockevent_set_mode(enum clock_event_mode mode, + struct clock_event_device *evt) +{ + switch (mode) { + case CLOCK_EVT_MODE_UNUSED: + case CLOCK_EVT_MODE_SHUTDOWN: + /* A 0 argument shuts the clock down. */ + hcall(LHCALL_SET_CLOCKEVENT, 0, 0, 0, 0); + break; + case CLOCK_EVT_MODE_ONESHOT: + /* This is what we expect. */ + break; + case CLOCK_EVT_MODE_PERIODIC: + BUG(); + case CLOCK_EVT_MODE_RESUME: + break; + } +} + +/* This describes our primitive timer chip. */ +static struct clock_event_device lguest_clockevent = { + .name = "lguest", + .features = CLOCK_EVT_FEAT_ONESHOT, + .set_next_event = lguest_clockevent_set_next_event, + .set_mode = lguest_clockevent_set_mode, + .rating = INT_MAX, + .mult = 1, + .shift = 0, + .min_delta_ns = LG_CLOCK_MIN_DELTA, + .max_delta_ns = LG_CLOCK_MAX_DELTA, +}; + +/* + * This is the Guest timer interrupt handler (hardware interrupt 0). We just + * call the clockevent infrastructure and it does whatever needs doing. + */ +static void lguest_time_irq(unsigned int irq, struct irq_desc *desc) +{ + unsigned long flags; + + /* Don't interrupt us while this is running. */ + local_irq_save(flags); + lguest_clockevent.event_handler(&lguest_clockevent); + local_irq_restore(flags); +} + +/* + * At some point in the boot process, we get asked to set up our timing + * infrastructure. The kernel doesn't expect timer interrupts before this, but + * we cleverly initialized the "blocked_interrupts" field of "struct + * lguest_data" so that timer interrupts were blocked until now. + */ +static void lguest_time_init(void) +{ + /* Set up the timer interrupt (0) to go to our simple timer routine */ + lguest_setup_irq(0); + irq_set_handler(0, lguest_time_irq); + + clocksource_register_hz(&lguest_clock, NSEC_PER_SEC); + + /* We can't set cpumask in the initializer: damn C limitations! Set it + * here and register our timer device. */ + lguest_clockevent.cpumask = cpumask_of(0); + clockevents_register_device(&lguest_clockevent); + + /* Finally, we unblock the timer interrupt. */ + clear_bit(0, lguest_data.blocked_interrupts); +} + +/* + * Miscellaneous bits and pieces. + * + * Here is an oddball collection of functions which the Guest needs for things + * to work. They're pretty simple. + */ + +/* + * The Guest needs to tell the Host what stack it expects traps to use. For + * native hardware, this is part of the Task State Segment mentioned above in + * lguest_load_tr_desc(), but to help hypervisors there's this special call. + * + * We tell the Host the segment we want to use (__KERNEL_DS is the kernel data + * segment), the privilege level (we're privilege level 1, the Host is 0 and + * will not tolerate us trying to use that), the stack pointer, and the number + * of pages in the stack. + */ +static void lguest_load_sp0(struct tss_struct *tss, + struct thread_struct *thread) +{ + lazy_hcall3(LHCALL_SET_STACK, __KERNEL_DS | 0x1, thread->sp0, + THREAD_SIZE / PAGE_SIZE); + tss->x86_tss.sp0 = thread->sp0; +} + +/* Let's just say, I wouldn't do debugging under a Guest. */ +static unsigned long lguest_get_debugreg(int regno) +{ + /* FIXME: Implement */ + return 0; +} + +static void lguest_set_debugreg(int regno, unsigned long value) +{ + /* FIXME: Implement */ +} + +/* + * There are times when the kernel wants to make sure that no memory writes are + * caught in the cache (that they've all reached real hardware devices). This + * doesn't matter for the Guest which has virtual hardware. + * + * On the Pentium 4 and above, cpuid() indicates that the Cache Line Flush + * (clflush) instruction is available and the kernel uses that. Otherwise, it + * uses the older "Write Back and Invalidate Cache" (wbinvd) instruction. + * Unlike clflush, wbinvd can only be run at privilege level 0. So we can + * ignore clflush, but replace wbinvd. + */ +static void lguest_wbinvd(void) +{ +} + +/* + * If the Guest expects to have an Advanced Programmable Interrupt Controller, + * we play dumb by ignoring writes and returning 0 for reads. So it's no + * longer Programmable nor Controlling anything, and I don't think 8 lines of + * code qualifies for Advanced. It will also never interrupt anything. It + * does, however, allow us to get through the Linux boot code. + */ +#ifdef CONFIG_X86_LOCAL_APIC +static void lguest_apic_write(u32 reg, u32 v) +{ +} + +static u32 lguest_apic_read(u32 reg) +{ + return 0; +} + +static u64 lguest_apic_icr_read(void) +{ + return 0; +} + +static void lguest_apic_icr_write(u32 low, u32 id) +{ + /* Warn to see if there's any stray references */ + WARN_ON(1); +} + +static void lguest_apic_wait_icr_idle(void) +{ + return; +} + +static u32 lguest_apic_safe_wait_icr_idle(void) +{ + return 0; +} + +static void set_lguest_basic_apic_ops(void) +{ + apic->read = lguest_apic_read; + apic->write = lguest_apic_write; + apic->icr_read = lguest_apic_icr_read; + apic->icr_write = lguest_apic_icr_write; + apic->wait_icr_idle = lguest_apic_wait_icr_idle; + apic->safe_wait_icr_idle = lguest_apic_safe_wait_icr_idle; +}; +#endif + +/* STOP! Until an interrupt comes in. */ +static void lguest_safe_halt(void) +{ + hcall(LHCALL_HALT, 0, 0, 0, 0); +} + +/* + * The SHUTDOWN hypercall takes a string to describe what's happening, and + * an argument which says whether this to restart (reboot) the Guest or not. + * + * Note that the Host always prefers that the Guest speak in physical addresses + * rather than virtual addresses, so we use __pa() here. + */ +static void lguest_power_off(void) +{ + hcall(LHCALL_SHUTDOWN, __pa("Power down"), + LGUEST_SHUTDOWN_POWEROFF, 0, 0); +} + +/* + * Panicing. + * + * Don't. But if you did, this is what happens. + */ +static int lguest_panic(struct notifier_block *nb, unsigned long l, void *p) +{ + hcall(LHCALL_SHUTDOWN, __pa(p), LGUEST_SHUTDOWN_POWEROFF, 0, 0); + /* The hcall won't return, but to keep gcc happy, we're "done". */ + return NOTIFY_DONE; +} + +static struct notifier_block paniced = { + .notifier_call = lguest_panic +}; + +/* Setting up memory is fairly easy. */ +static __init char *lguest_memory_setup(void) +{ + /* + * The Linux bootloader header contains an "e820" memory map: the + * Launcher populated the first entry with our memory limit. + */ + e820_add_region(boot_params.e820_map[0].addr, + boot_params.e820_map[0].size, + boot_params.e820_map[0].type); + + /* This string is for the boot messages. */ + return "LGUEST"; +} + +/* Offset within PCI config space of BAR access capability. */ +static int console_cfg_offset = 0; +static int console_access_cap; + +/* Set up so that we access off in bar0 (on bus 0, device 1, function 0) */ +static void set_cfg_window(u32 cfg_offset, u32 off) +{ + write_pci_config_byte(0, 1, 0, + cfg_offset + offsetof(struct virtio_pci_cap, bar), + 0); + write_pci_config(0, 1, 0, + cfg_offset + offsetof(struct virtio_pci_cap, length), + 4); + write_pci_config(0, 1, 0, + cfg_offset + offsetof(struct virtio_pci_cap, offset), + off); +} + +static void write_bar_via_cfg(u32 cfg_offset, u32 off, u32 val) +{ + /* + * We could set this up once, then leave it; nothing else in the * + * kernel should touch these registers. But if it went wrong, that + * would be a horrible bug to find. + */ + set_cfg_window(cfg_offset, off); + write_pci_config(0, 1, 0, + cfg_offset + sizeof(struct virtio_pci_cap), val); +} + +static void probe_pci_console(void) +{ + u8 cap, common_cap = 0, device_cap = 0; + /* Offset within BAR0 */ + u32 device_offset; + u32 device_len; + + /* Avoid recursive printk into here. */ + console_cfg_offset = -1; + + if (!early_pci_allowed()) { + printk(KERN_ERR "lguest: early PCI access not allowed!\n"); + return; + } + + /* We expect a console PCI device at BUS0, slot 1. */ + if (read_pci_config(0, 1, 0, 0) != 0x10431AF4) { + printk(KERN_ERR "lguest: PCI device is %#x!\n", + read_pci_config(0, 1, 0, 0)); + return; + } + + /* Find the capabilities we need (must be in bar0) */ + cap = read_pci_config_byte(0, 1, 0, PCI_CAPABILITY_LIST); + while (cap) { + u8 vndr = read_pci_config_byte(0, 1, 0, cap); + if (vndr == PCI_CAP_ID_VNDR) { + u8 type, bar; + u32 offset, length; + + type = read_pci_config_byte(0, 1, 0, + cap + offsetof(struct virtio_pci_cap, cfg_type)); + bar = read_pci_config_byte(0, 1, 0, + cap + offsetof(struct virtio_pci_cap, bar)); + offset = read_pci_config(0, 1, 0, + cap + offsetof(struct virtio_pci_cap, offset)); + length = read_pci_config(0, 1, 0, + cap + offsetof(struct virtio_pci_cap, length)); + + switch (type) { + case VIRTIO_PCI_CAP_DEVICE_CFG: + if (bar == 0) { + device_cap = cap; + device_offset = offset; + device_len = length; + } + break; + case VIRTIO_PCI_CAP_PCI_CFG: + console_access_cap = cap; + break; + } + } + cap = read_pci_config_byte(0, 1, 0, cap + PCI_CAP_LIST_NEXT); + } + if (!device_cap || !console_access_cap) { + printk(KERN_ERR "lguest: No caps (%u/%u/%u) in console!\n", + common_cap, device_cap, console_access_cap); + return; + } + + /* + * Note that we can't check features, until we've set the DRIVER + * status bit. We don't want to do that until we have a real driver, + * so we just check that the device-specific config has room for + * emerg_wr. If it doesn't support VIRTIO_CONSOLE_F_EMERG_WRITE + * it should ignore the access. + */ + if (device_len < (offsetof(struct virtio_console_config, emerg_wr) + + sizeof(u32))) { + printk(KERN_ERR "lguest: console missing emerg_wr field\n"); + return; + } + + console_cfg_offset = device_offset; + printk(KERN_INFO "lguest: Console via virtio-pci emerg_wr\n"); +} + +/* + * We will eventually use the virtio console device to produce console output, + * but before that is set up we use the virtio PCI console's backdoor mmio + * access and the "emergency" write facility (which is legal even before the + * device is configured). + */ +static __init int early_put_chars(u32 vtermno, const char *buf, int count) +{ + /* If we couldn't find PCI console, forget it. */ + if (console_cfg_offset < 0) + return count; + + if (unlikely(!console_cfg_offset)) { + probe_pci_console(); + if (console_cfg_offset < 0) + return count; + } + + write_bar_via_cfg(console_access_cap, + console_cfg_offset + + offsetof(struct virtio_console_config, emerg_wr), + buf[0]); + return 1; +} + +/* + * Rebooting also tells the Host we're finished, but the RESTART flag tells the + * Launcher to reboot us. + */ +static void lguest_restart(char *reason) +{ + hcall(LHCALL_SHUTDOWN, __pa(reason), LGUEST_SHUTDOWN_RESTART, 0, 0); +} + +/*G:050 + * Patching (Powerfully Placating Performance Pedants) + * + * We have already seen that pv_ops structures let us replace simple native + * instructions with calls to the appropriate back end all throughout the + * kernel. This allows the same kernel to run as a Guest and as a native + * kernel, but it's slow because of all the indirect branches. + * + * Remember that David Wheeler quote about "Any problem in computer science can + * be solved with another layer of indirection"? The rest of that quote is + * "... But that usually will create another problem." This is the first of + * those problems. + * + * Our current solution is to allow the paravirt back end to optionally patch + * over the indirect calls to replace them with something more efficient. We + * patch two of the simplest of the most commonly called functions: disable + * interrupts and save interrupts. We usually have 6 or 10 bytes to patch + * into: the Guest versions of these operations are small enough that we can + * fit comfortably. + * + * First we need assembly templates of each of the patchable Guest operations, + * and these are in head_32.S. + */ + +/*G:060 We construct a table from the assembler templates: */ +static const struct lguest_insns +{ + const char *start, *end; +} lguest_insns[] = { + [PARAVIRT_PATCH(pv_irq_ops.irq_disable)] = { lgstart_cli, lgend_cli }, + [PARAVIRT_PATCH(pv_irq_ops.save_fl)] = { lgstart_pushf, lgend_pushf }, +}; + +/* + * Now our patch routine is fairly simple (based on the native one in + * paravirt.c). If we have a replacement, we copy it in and return how much of + * the available space we used. + */ +static unsigned lguest_patch(u8 type, u16 clobber, void *ibuf, + unsigned long addr, unsigned len) +{ + unsigned int insn_len; + + /* Don't do anything special if we don't have a replacement */ + if (type >= ARRAY_SIZE(lguest_insns) || !lguest_insns[type].start) + return paravirt_patch_default(type, clobber, ibuf, addr, len); + + insn_len = lguest_insns[type].end - lguest_insns[type].start; + + /* Similarly if it can't fit (doesn't happen, but let's be thorough). */ + if (len < insn_len) + return paravirt_patch_default(type, clobber, ibuf, addr, len); + + /* Copy in our instructions. */ + memcpy(ibuf, lguest_insns[type].start, insn_len); + return insn_len; +} + +/*G:029 + * Once we get to lguest_init(), we know we're a Guest. The various + * pv_ops structures in the kernel provide points for (almost) every routine we + * have to override to avoid privileged instructions. + */ +__init void lguest_init(void) +{ + /* We're under lguest. */ + pv_info.name = "lguest"; + /* Paravirt is enabled. */ + pv_info.paravirt_enabled = 1; + /* We're running at privilege level 1, not 0 as normal. */ + pv_info.kernel_rpl = 1; + /* Everyone except Xen runs with this set. */ + pv_info.shared_kernel_pmd = 1; + + /* + * We set up all the lguest overrides for sensitive operations. These + * are detailed with the operations themselves. + */ + + /* Interrupt-related operations */ + pv_irq_ops.save_fl = PV_CALLEE_SAVE(lguest_save_fl); + pv_irq_ops.restore_fl = __PV_IS_CALLEE_SAVE(lg_restore_fl); + pv_irq_ops.irq_disable = PV_CALLEE_SAVE(lguest_irq_disable); + pv_irq_ops.irq_enable = __PV_IS_CALLEE_SAVE(lg_irq_enable); + pv_irq_ops.safe_halt = lguest_safe_halt; + + /* Setup operations */ + pv_init_ops.patch = lguest_patch; + + /* Intercepts of various CPU instructions */ + pv_cpu_ops.load_gdt = lguest_load_gdt; + pv_cpu_ops.cpuid = lguest_cpuid; + pv_cpu_ops.load_idt = lguest_load_idt; + pv_cpu_ops.iret = lguest_iret; + pv_cpu_ops.load_sp0 = lguest_load_sp0; + pv_cpu_ops.load_tr_desc = lguest_load_tr_desc; + pv_cpu_ops.set_ldt = lguest_set_ldt; + pv_cpu_ops.load_tls = lguest_load_tls; + pv_cpu_ops.get_debugreg = lguest_get_debugreg; + pv_cpu_ops.set_debugreg = lguest_set_debugreg; + pv_cpu_ops.clts = lguest_clts; + pv_cpu_ops.read_cr0 = lguest_read_cr0; + pv_cpu_ops.write_cr0 = lguest_write_cr0; + pv_cpu_ops.read_cr4 = lguest_read_cr4; + pv_cpu_ops.write_cr4 = lguest_write_cr4; + pv_cpu_ops.write_gdt_entry = lguest_write_gdt_entry; + pv_cpu_ops.write_idt_entry = lguest_write_idt_entry; + pv_cpu_ops.wbinvd = lguest_wbinvd; + pv_cpu_ops.start_context_switch = paravirt_start_context_switch; + pv_cpu_ops.end_context_switch = lguest_end_context_switch; + + /* Pagetable management */ + pv_mmu_ops.write_cr3 = lguest_write_cr3; + pv_mmu_ops.flush_tlb_user = lguest_flush_tlb_user; + pv_mmu_ops.flush_tlb_single = lguest_flush_tlb_single; + pv_mmu_ops.flush_tlb_kernel = lguest_flush_tlb_kernel; + pv_mmu_ops.set_pte = lguest_set_pte; + pv_mmu_ops.set_pte_at = lguest_set_pte_at; + pv_mmu_ops.set_pmd = lguest_set_pmd; +#ifdef CONFIG_X86_PAE + pv_mmu_ops.set_pte_atomic = lguest_set_pte_atomic; + pv_mmu_ops.pte_clear = lguest_pte_clear; + pv_mmu_ops.pmd_clear = lguest_pmd_clear; + pv_mmu_ops.set_pud = lguest_set_pud; +#endif + pv_mmu_ops.read_cr2 = lguest_read_cr2; + pv_mmu_ops.read_cr3 = lguest_read_cr3; + pv_mmu_ops.lazy_mode.enter = paravirt_enter_lazy_mmu; + pv_mmu_ops.lazy_mode.leave = lguest_leave_lazy_mmu_mode; + pv_mmu_ops.lazy_mode.flush = paravirt_flush_lazy_mmu; + pv_mmu_ops.pte_update = lguest_pte_update; + pv_mmu_ops.pte_update_defer = lguest_pte_update; + +#ifdef CONFIG_X86_LOCAL_APIC + /* APIC read/write intercepts */ + set_lguest_basic_apic_ops(); +#endif + + x86_init.resources.memory_setup = lguest_memory_setup; + x86_init.irqs.intr_init = lguest_init_IRQ; + x86_init.timers.timer_init = lguest_time_init; + x86_platform.calibrate_tsc = lguest_tsc_khz; + x86_platform.get_wallclock = lguest_get_wallclock; + + /* + * Now is a good time to look at the implementations of these functions + * before returning to the rest of lguest_init(). + */ + + /*G:070 + * Now we've seen all the paravirt_ops, we return to + * lguest_init() where the rest of the fairly chaotic boot setup + * occurs. + */ + + /* + * The stack protector is a weird thing where gcc places a canary + * value on the stack and then checks it on return. This file is + * compiled with -fno-stack-protector it, so we got this far without + * problems. The value of the canary is kept at offset 20 from the + * %gs register, so we need to set that up before calling C functions + * in other files. + */ + setup_stack_canary_segment(0); + + /* + * We could just call load_stack_canary_segment(), but we might as well + * call switch_to_new_gdt() which loads the whole table and sets up the + * per-cpu segment descriptor register %fs as well. + */ + switch_to_new_gdt(0); + + /* + * The Host<->Guest Switcher lives at the top of our address space, and + * the Host told us how big it is when we made LGUEST_INIT hypercall: + * it put the answer in lguest_data.reserve_mem + */ + reserve_top_address(lguest_data.reserve_mem); + + /* + * If we don't initialize the lock dependency checker now, it crashes + * atomic_notifier_chain_register, then paravirt_disable_iospace. + */ + lockdep_init(); + + /* Hook in our special panic hypercall code. */ + atomic_notifier_chain_register(&panic_notifier_list, &paniced); + + /* + * This is messy CPU setup stuff which the native boot code does before + * start_kernel, so we have to do, too: + */ + cpu_detect(&new_cpu_data); + /* head.S usually sets up the first capability word, so do it here. */ + new_cpu_data.x86_capability[0] = cpuid_edx(1); + + /* Math is always hard! */ + set_cpu_cap(&new_cpu_data, X86_FEATURE_FPU); + + /* We don't have features. We have puppies! Puppies! */ +#ifdef CONFIG_X86_MCE + mca_cfg.disabled = true; +#endif +#ifdef CONFIG_ACPI + acpi_disabled = 1; +#endif + + /* + * We set the preferred console to "hvc". This is the "hypervisor + * virtual console" driver written by the PowerPC people, which we also + * adapted for lguest's use. + */ + add_preferred_console("hvc", 0, NULL); + + /* Register our very early console. */ + virtio_cons_early_init(early_put_chars); + + /* Don't let ACPI try to control our PCI interrupts. */ + disable_acpi(); + + /* We control them ourselves, by overriding these two hooks. */ + pcibios_enable_irq = lguest_enable_irq; + pcibios_disable_irq = lguest_disable_irq; + + /* + * Last of all, we set the power management poweroff hook to point to + * the Guest routine to power off, and the reboot hook to our restart + * routine. + */ + pm_power_off = lguest_power_off; + machine_ops.restart = lguest_restart; + + /* + * Now we're set up, call i386_start_kernel() in head32.c and we proceed + * to boot as normal. It never returns. + */ + i386_start_kernel(); +} +/* + * This marks the end of stage II of our journey, The Guest. + * + * It is now time for us to explore the layer of virtual drivers and complete + * our understanding of the Guest in "make Drivers". + */ diff --git a/kernel/arch/x86/lguest/head_32.S b/kernel/arch/x86/lguest/head_32.S new file mode 100644 index 000000000..d5ae63f5e --- /dev/null +++ b/kernel/arch/x86/lguest/head_32.S @@ -0,0 +1,192 @@ +#include <linux/linkage.h> +#include <linux/lguest.h> +#include <asm/lguest_hcall.h> +#include <asm/asm-offsets.h> +#include <asm/thread_info.h> +#include <asm/processor-flags.h> + +/*G:020 + + * Our story starts with the bzImage: booting starts at startup_32 in + * arch/x86/boot/compressed/head_32.S. This merely uncompresses the real + * kernel in place and then jumps into it: startup_32 in + * arch/x86/kernel/head_32.S. Both routines expects a boot header in the %esi + * register, which is created by the bootloader (the Launcher in our case). + * + * The startup_32 function does very little: it clears the uninitialized global + * C variables which we expect to be zero (ie. BSS) and then copies the boot + * header and kernel command line somewhere safe, and populates some initial + * page tables. Finally it checks the 'hardware_subarch' field. This was + * introduced in 2.6.24 for lguest and Xen: if it's set to '1' (lguest's + * assigned number), then it calls us here. + * + * WARNING: be very careful here! We're running at addresses equal to physical + * addresses (around 0), not above PAGE_OFFSET as most code expects + * (eg. 0xC0000000). Jumps are relative, so they're OK, but we can't touch any + * data without remembering to subtract __PAGE_OFFSET! + * + * The .section line puts this code in .init.text so it will be discarded after + * boot. + */ +.section .init.text, "ax", @progbits +ENTRY(lguest_entry) + /* + * We make the "initialization" hypercall now to tell the Host where + * our lguest_data struct is. + */ + movl $LHCALL_LGUEST_INIT, %eax + movl $lguest_data - __PAGE_OFFSET, %ebx + int $LGUEST_TRAP_ENTRY + + /* Now turn our pagetables on; setup by arch/x86/kernel/head_32.S. */ + movl $LHCALL_NEW_PGTABLE, %eax + movl $(initial_page_table - __PAGE_OFFSET), %ebx + int $LGUEST_TRAP_ENTRY + + /* Set up the initial stack so we can run C code. */ + movl $(init_thread_union+THREAD_SIZE),%esp + + /* Jumps are relative: we're running __PAGE_OFFSET too low. */ + jmp lguest_init+__PAGE_OFFSET + +/*G:055 + * We create a macro which puts the assembler code between lgstart_ and lgend_ + * markers. These templates are put in the .text section: they can't be + * discarded after boot as we may need to patch modules, too. + */ +.text +#define LGUEST_PATCH(name, insns...) \ + lgstart_##name: insns; lgend_##name:; \ + .globl lgstart_##name; .globl lgend_##name + +LGUEST_PATCH(cli, movl $0, lguest_data+LGUEST_DATA_irq_enabled) +LGUEST_PATCH(pushf, movl lguest_data+LGUEST_DATA_irq_enabled, %eax) + +/*G:033 + * But using those wrappers is inefficient (we'll see why that doesn't matter + * for save_fl and irq_disable later). If we write our routines carefully in + * assembler, we can avoid clobbering any registers and avoid jumping through + * the wrapper functions. + * + * I skipped over our first piece of assembler, but this one is worth studying + * in a bit more detail so I'll describe in easy stages. First, the routine to + * enable interrupts: + */ +ENTRY(lg_irq_enable) + /* + * The reverse of irq_disable, this sets lguest_data.irq_enabled to + * X86_EFLAGS_IF (ie. "Interrupts enabled"). + */ + movl $X86_EFLAGS_IF, lguest_data+LGUEST_DATA_irq_enabled + /* + * But now we need to check if the Host wants to know: there might have + * been interrupts waiting to be delivered, in which case it will have + * set lguest_data.irq_pending to X86_EFLAGS_IF. If it's not zero, we + * jump to send_interrupts, otherwise we're done. + */ + cmpl $0, lguest_data+LGUEST_DATA_irq_pending + jnz send_interrupts + /* + * One cool thing about x86 is that you can do many things without using + * a register. In this case, the normal path hasn't needed to save or + * restore any registers at all! + */ + ret +send_interrupts: + /* + * OK, now we need a register: eax is used for the hypercall number, + * which is LHCALL_SEND_INTERRUPTS. + * + * We used not to bother with this pending detection at all, which was + * much simpler. Sooner or later the Host would realize it had to + * send us an interrupt. But that turns out to make performance 7 + * times worse on a simple tcp benchmark. So now we do this the hard + * way. + */ + pushl %eax + movl $LHCALL_SEND_INTERRUPTS, %eax + /* This is the actual hypercall trap. */ + int $LGUEST_TRAP_ENTRY + /* Put eax back the way we found it. */ + popl %eax + ret + +/* + * Finally, the "popf" or "restore flags" routine. The %eax register holds the + * flags (in practice, either X86_EFLAGS_IF or 0): if it's X86_EFLAGS_IF we're + * enabling interrupts again, if it's 0 we're leaving them off. + */ +ENTRY(lg_restore_fl) + /* This is just "lguest_data.irq_enabled = flags;" */ + movl %eax, lguest_data+LGUEST_DATA_irq_enabled + /* + * Now, if the %eax value has enabled interrupts and + * lguest_data.irq_pending is set, we want to tell the Host so it can + * deliver any outstanding interrupts. Fortunately, both values will + * be X86_EFLAGS_IF (ie. 512) in that case, and the "testl" + * instruction will AND them together for us. If both are set, we + * jump to send_interrupts. + */ + testl lguest_data+LGUEST_DATA_irq_pending, %eax + jnz send_interrupts + /* Again, the normal path has used no extra registers. Clever, huh? */ + ret +/*:*/ + +/* These demark the EIP where host should never deliver interrupts. */ +.global lguest_noirq_iret + +/*M:004 + * When the Host reflects a trap or injects an interrupt into the Guest, it + * sets the eflags interrupt bit on the stack based on lguest_data.irq_enabled, + * so the Guest iret logic does the right thing when restoring it. However, + * when the Host sets the Guest up for direct traps, such as system calls, the + * processor is the one to push eflags onto the stack, and the interrupt bit + * will be 1 (in reality, interrupts are always enabled in the Guest). + * + * This turns out to be harmless: the only trap which should happen under Linux + * with interrupts disabled is Page Fault (due to our lazy mapping of vmalloc + * regions), which has to be reflected through the Host anyway. If another + * trap *does* go off when interrupts are disabled, the Guest will panic, and + * we'll never get to this iret! +:*/ + +/*G:045 + * There is one final paravirt_op that the Guest implements, and glancing at it + * you can see why I left it to last. It's *cool*! It's in *assembler*! + * + * The "iret" instruction is used to return from an interrupt or trap. The + * stack looks like this: + * old address + * old code segment & privilege level + * old processor flags ("eflags") + * + * The "iret" instruction pops those values off the stack and restores them all + * at once. The only problem is that eflags includes the Interrupt Flag which + * the Guest can't change: the CPU will simply ignore it when we do an "iret". + * So we have to copy eflags from the stack to lguest_data.irq_enabled before + * we do the "iret". + * + * There are two problems with this: firstly, we can't clobber any registers + * and secondly, the whole thing needs to be atomic. The first problem + * is solved by using "push memory"/"pop memory" instruction pair for copying. + * + * The second is harder: copying eflags to lguest_data.irq_enabled will turn + * interrupts on before we're finished, so we could be interrupted before we + * return to userspace or wherever. Our solution to this is to tell the + * Host that it is *never* to interrupt us there, even if interrupts seem to be + * enabled. (It's not necessary to protect pop instruction, since + * data gets updated only after it completes, so we only need to protect + * one instruction, iret). + */ +ENTRY(lguest_iret) + pushl 2*4(%esp) + /* + * Note the %ss: segment prefix here. Normal data accesses use the + * "ds" segment, but that will have already been restored for whatever + * we're returning to (such as userspace): we can't trust it. The %ss: + * prefix makes sure we use the stack segment, which is still valid. + */ + popl %ss:lguest_data+LGUEST_DATA_irq_enabled +lguest_noirq_iret: + iret |