From 9ca8dbcc65cfc63d6f5ef3312a33184e1d726e00 Mon Sep 17 00:00:00 2001 From: Yunhong Jiang Date: Tue, 4 Aug 2015 12:17:53 -0700 Subject: Add the rt linux 4.1.3-rt3 as base Import the rt linux 4.1.3-rt3 as OPNFV kvm base. It's from git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git linux-4.1.y-rt and the base is: commit 0917f823c59692d751951bf5ea699a2d1e2f26a2 Author: Sebastian Andrzej Siewior Date: Sat Jul 25 12:13:34 2015 +0200 Prepare v4.1.3-rt3 Signed-off-by: Sebastian Andrzej Siewior We lose all the git history this way and it's not good. We should apply another opnfv project repo in future. Change-Id: I87543d81c9df70d99c5001fbdf646b202c19f423 Signed-off-by: Yunhong Jiang --- kernel/Documentation/arm64/tagged-pointers.txt | 34 ++++++++++++++++++++++++++ 1 file changed, 34 insertions(+) create mode 100644 kernel/Documentation/arm64/tagged-pointers.txt (limited to 'kernel/Documentation/arm64/tagged-pointers.txt') diff --git a/kernel/Documentation/arm64/tagged-pointers.txt b/kernel/Documentation/arm64/tagged-pointers.txt new file mode 100644 index 000000000..d9995f1f5 --- /dev/null +++ b/kernel/Documentation/arm64/tagged-pointers.txt @@ -0,0 +1,34 @@ + Tagged virtual addresses in AArch64 Linux + ========================================= + +Author: Will Deacon +Date : 12 June 2013 + +This document briefly describes the provision of tagged virtual +addresses in the AArch64 translation system and their potential uses +in AArch64 Linux. + +The kernel configures the translation tables so that translations made +via TTBR0 (i.e. userspace mappings) have the top byte (bits 63:56) of +the virtual address ignored by the translation hardware. This frees up +this byte for application use, with the following caveats: + + (1) The kernel requires that all user addresses passed to EL1 + are tagged with tag 0x00. This means that any syscall + parameters containing user virtual addresses *must* have + their top byte cleared before trapping to the kernel. + + (2) Non-zero tags are not preserved when delivering signals. + This means that signal handlers in applications making use + of tags cannot rely on the tag information for user virtual + addresses being maintained for fields inside siginfo_t. + One exception to this rule is for signals raised in response + to watchpoint debug exceptions, where the tag information + will be preserved. + + (3) Special care should be taken when using tagged pointers, + since it is likely that C compilers will not hazard two + virtual addresses differing only in the upper byte. + +The architecture prevents the use of a tagged PC, so the upper byte will +be set to a sign-extension of bit 55 on exception return. -- cgit 1.2.3-korg