tree f6bf34cb9ad1e4ec85c8ef2a11ddee9d24c73d9a
parent 72016f3a4221799a0b1fdf443ef6e29db572a9bb
author Avi Kivity <avi@redhat.com> 1268654394 +0200
committer Avi Kivity <avi@redhat.com> 1274087739 +0300

KVM: Make locked operations truly atomic

Once upon a time, locked operations were emulated while holding the mmu mutex.
Since mmu pages were write protected, it was safe to emulate the writes in
a non-atomic manner, since there could be no other writer, either in the
guest or in the kernel.

These days emulation takes place without holding the mmu spinlock, so the
write could be preempted by an unshadowing event, which exposes the page
to writes by the guest.  This may cause corruption of guest page tables.

Fix by using an atomic cmpxchg for these operations.

Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>