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[Qemu-devel] [PATCH] migration: initialize RAM to zero
From: |
Paolo Bonzini |
Subject: |
[Qemu-devel] [PATCH] migration: initialize RAM to zero |
Date: |
Mon, 8 Apr 2013 12:47:08 +0200 |
Using qemu_memalign only leaves the RAM zero by chance, because libc
will usually use mmap to satisfy our huge requests. But memory will
not be zero when using MALLOC_PERTURB_ with a nonzero value. In the
case of incoming migration, this breaks a recently-introduced
invariant (commit f1c7279, migration: do not sent zero pages in
bulk stage, 2013-03-26).
To fix this, use mmap ourselves to get a well-aligned, always zero
block for the RAM. Mmap-ed memory is easy to "trim" at the sides.
This also removes the need to do something special on valgrind
(see commit c2a8238a, Support running QEMU on Valgrind, 2011-10-31).
Signed-off-by: Paolo Bonzini <address@hidden>
---
util/oslib-posix.c | 30 +++++++++++++-----------------
1 file changed, 13 insertions(+), 17 deletions(-)
diff --git a/util/oslib-posix.c b/util/oslib-posix.c
index 433dd68..91f5aab 100644
--- a/util/oslib-posix.c
+++ b/util/oslib-posix.c
@@ -52,12 +52,8 @@ extern int daemon(int, int);
#include "sysemu/sysemu.h"
#include "trace.h"
#include "qemu/sockets.h"
+#include <sys/mman.h>
-#if defined(CONFIG_VALGRIND)
-static int running_on_valgrind = -1;
-#else
-# define running_on_valgrind 0
-#endif
#ifdef CONFIG_LINUX
#include <sys/syscall.h>
#endif
@@ -108,22 +104,22 @@ void *qemu_memalign(size_t alignment, size_t size)
/* alloc shared memory pages */
void *qemu_vmalloc(size_t size)
{
- void *ptr;
size_t align = QEMU_VMALLOC_ALIGN;
+ size_t total = size + align - getpagesize();
+ void *ptr = mmap(0, total, PROT_READ | PROT_WRITE,
+ MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+ size_t offset = QEMU_ALIGN_UP((uintptr_t)ptr, align) - (uintptr_t)ptr;
-#if defined(CONFIG_VALGRIND)
- if (running_on_valgrind < 0) {
- /* First call, test whether we are running on Valgrind.
- This is a substitute for RUNNING_ON_VALGRIND from valgrind.h. */
- const char *ld = getenv("LD_PRELOAD");
- running_on_valgrind = (ld != NULL && strstr(ld, "vgpreload"));
- }
-#endif
+ ptr += offset;
+ total -= offset;
- if (size < align || running_on_valgrind) {
- align = getpagesize();
+ if (offset > 0) {
+ munmap(ptr - offset, offset);
+ }
+ if (total > size) {
+ munmap(ptr + size, total - size);
}
- ptr = qemu_memalign(align, size);
+
trace_qemu_vmalloc(size, ptr);
return ptr;
}
--
1.8.1.4
- [Qemu-devel] [PATCH] migration: initialize RAM to zero,
Paolo Bonzini <=