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 <pbonz...@redhat.com> --- 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