From patchwork Mon Feb 4 10:41:10 2013 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: [60/60] migration: Fix madvise breakage if host and guest have different page sizes From: Michael Tokarev X-Patchwork-Id: 217956 Message-Id: <1359974470-17044-61-git-send-email-mjt@msgid.tls.msk.ru> To: qemu-devel@nongnu.org Cc: Anthony Liguori , Michael Tokarev , qemu-stable@nongnu.org, David Gibson Date: Mon, 4 Feb 2013 14:41:10 +0400 From: David Gibson madvise(DONTNEED) will throw away the contents of the whole page at the given address, even if the given length is less than the page size. One can argue about whether that's the correct behaviour, but that's what it's done for a long time in Linux at least. That means that the madvise() in ram_load(), on a setup where TARGET_PAGE_SIZE is smaller than the host page size, can throw away data in guest pages adjacent to the one it's actually processing right now, leading to guest memory corruption on an incoming migration. This patch therefore, disables the madvise() if the host page size is larger than TARGET_PAGE_SIZE. This means we don't get the benefits of that madvise() in this case, but a more complete fix is more difficult to accomplish. This at least fixes the guest memory corruption. Signed-off-by: David Gibson Reported-by: Alexey Kardashevskiy Signed-off-by: Anthony Liguori (cherry picked from commit 45e6cee42b98d10e2e14885ab656541a9ffd5187) Signed-off-by: Michael Tokarev --- arch_init.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch_init.c b/arch_init.c index a9e8b74..a1c3cfb 100644 --- a/arch_init.c +++ b/arch_init.c @@ -475,7 +475,8 @@ int ram_load(QEMUFile *f, void *opaque, int version_id) memset(host, ch, TARGET_PAGE_SIZE); #ifndef _WIN32 if (ch == 0 && - (!kvm_enabled() || kvm_has_sync_mmu())) { + (!kvm_enabled() || kvm_has_sync_mmu()) && + getpagesize() <= TARGET_PAGE_SIZE) { qemu_madvise(host, TARGET_PAGE_SIZE, QEMU_MADV_DONTNEED); } #endif