KVM: x86: emulator_cmpxchg_emulated should mark_page_dirty

[Marcelo Tosatti <mtosatti@redhat.com>]

emulator_cmpxchg_emulated writes to guest memory, therefore it should
updated the dirty bitmap accordingly.

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

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 39c28f09..29db96d 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4394,6 +4394,7 @@ static int emulator_cmpxchg_emulated(struct x86_emulate_ctxt *ctxt,
 	if (!exchanged)
 		return X86EMUL_CMPXCHG_FAILED;
 
+	mark_page_dirty(vcpu->kvm, gpa >> PAGE_SHIFT);
 	kvm_mmu_pte_write(vcpu, gpa, new, bytes);
 
 	return X86EMUL_CONTINUE;