1 files changed, 110 insertions, 0 deletions
diff --git a/qemu/util/mmap-alloc.c b/qemu/util/mmap-alloc.c
new file mode 100644
index 000000000..0b4cc7f7f
--- /dev/null
+++ b/qemu/util/mmap-alloc.c
@@ -0,0 +1,110 @@
+/*
+ * Support for RAM backed by mmaped host memory.
+ *
+ * Copyright (c) 2015 Red Hat, Inc.
+ *
+ * Authors:
+ *  Michael S. Tsirkin <mst@redhat.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or
+ * later.  See the COPYING file in the top-level directory.
+ */
+#include "qemu/osdep.h"
+#include <qemu/mmap-alloc.h>
+#include <sys/mman.h>
+
+#define HUGETLBFS_MAGIC       0x958458f6
+
+#ifdef CONFIG_LINUX
+#include <sys/vfs.h>
+#endif
+
+size_t qemu_fd_getpagesize(int fd)
+{
+#ifdef CONFIG_LINUX
+    struct statfs fs;
+    int ret;
+
+    if (fd != -1) {
+        do {
+            ret = fstatfs(fd, &fs);
+        } while (ret != 0 && errno == EINTR);
+
+        if (ret == 0 && fs.f_type == HUGETLBFS_MAGIC) {
+            return fs.f_bsize;
+        }
+    }
+#endif
+
+    return getpagesize();
+}
+
+void *qemu_ram_mmap(int fd, size_t size, size_t align, bool shared)
+{
+    /*
+     * Note: this always allocates at least one extra page of virtual address
+     * space, even if size is already aligned.
+     */
+    size_t total = size + align;
+#if defined(__powerpc64__) && defined(__linux__)
+    /* On ppc64 mappings in the same segment (aka slice) must share the same
+     * page size. Since we will be re-allocating part of this segment
+     * from the supplied fd, we should make sure to use the same page size, to
+     * this end we mmap the supplied fd.  In this case, set MAP_NORESERVE to
+     * avoid allocating backing store memory.
+     * We do this unless we are using the system page size, in which case
+     * anonymous memory is OK.
+     */
+    int anonfd = fd == -1 || qemu_fd_getpagesize(fd) == getpagesize() ? -1 : fd;
+    int flags = anonfd == -1 ? MAP_ANONYMOUS : MAP_NORESERVE;
+    void *ptr = mmap(0, total, PROT_NONE, flags | MAP_PRIVATE, anonfd, 0);
+#else
+    void *ptr = mmap(0, total, PROT_NONE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+#endif
+    size_t offset = QEMU_ALIGN_UP((uintptr_t)ptr, align) - (uintptr_t)ptr;
+    void *ptr1;
+
+    if (ptr == MAP_FAILED) {
+        return MAP_FAILED;
+    }
+
+    /* Make sure align is a power of 2 */
+    assert(!(align & (align - 1)));
+    /* Always align to host page size */
+    assert(align >= getpagesize());
+
+    ptr1 = mmap(ptr + offset, size, PROT_READ | PROT_WRITE,
+                MAP_FIXED |
+                (fd == -1 ? MAP_ANONYMOUS : 0) |
+                (shared ? MAP_SHARED : MAP_PRIVATE),
+                fd, 0);
+    if (ptr1 == MAP_FAILED) {
+        munmap(ptr, total);
+        return MAP_FAILED;
+    }
+
+    ptr += offset;
+    total -= offset;
+
+    if (offset > 0) {
+        munmap(ptr - offset, offset);
+    }
+
+    /*
+     * Leave a single PROT_NONE page allocated after the RAM block, to serve as
+     * a guard page guarding against potential buffer overflows.
+     */
+    if (total > size + getpagesize()) {
+        munmap(ptr + size + getpagesize(), total - size - getpagesize());
+    }
+
+    return ptr;
+}
+
+void qemu_ram_munmap(void *ptr, size_t size)
+{
+    if (ptr) {
+        /* Unmap both the RAM block and the guard page */
+        munmap(ptr, size + getpagesize());
+    }
+}