From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:51279) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Tb2Ng-0003NM-Ba for qemu-devel@nongnu.org; Tue, 20 Nov 2012 23:57:49 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Tb2Nf-00037O-6z for qemu-devel@nongnu.org; Tue, 20 Nov 2012 23:57:48 -0500 Received: from ozlabs.org ([2402:b800:7003:1:1::1]:40219) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Tb2Nd-00036G-Iz for qemu-devel@nongnu.org; Tue, 20 Nov 2012 23:57:47 -0500 From: David Gibson Date: Wed, 21 Nov 2012 15:59:25 +1100 Message-Id: <1353473965-30678-1-git-send-email-david@gibson.dropbear.id.au> Subject: [Qemu-devel] [PATCH] migration: Fix madvise breakage if host and guest have different page sizes List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org, quintela@redhat.com Cc: 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 --- arch_init.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch_init.c b/arch_init.c index b75a4c5..83dcc53 100644 --- a/arch_init.c +++ b/arch_init.c @@ -840,7 +840,8 @@ static 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 -- 1.7.10.4