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[Xen-changelog] [qemu-upstream-unstable] migration: Fix madvise breakage if host and guest have different page sizes

commit f1a2195ec327fd2b837a3539623ee431d133f03c
Author:     David Gibson <david@xxxxxxxxxxxxxxxxxxxxx>
AuthorDate: Tue Dec 4 11:38:39 2012 +1100
Commit:     Michael Roth <mdroth@xxxxxxxxxxxxxxxxxx>
CommitDate: Mon Jan 14 15:41:11 2013 -0600

    migration: Fix madvise breakage if host and guest have different page sizes
    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 <david@xxxxxxxxxxxxxxxxxxxxx>
    Reported-by: Alexey Kardashevskiy <aik@xxxxxxxxx>
    Signed-off-by: Anthony Liguori <aliguori@xxxxxxxxxx>
    (cherry picked from commit 45e6cee42b98d10e2e14885ab656541a9ffd5187)
    Signed-off-by: Michael Roth <mdroth@xxxxxxxxxxxxxxxxxx>
 arch_init.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

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 
             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);
generated by git-patchbot for /home/xen/git/qemu-upstream-unstable.git

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