KVM: MMU: don't atomicly set spte if it's not present

If the old mapping is not present, the spte.a is not lost, so no need
atomic operation to set it

Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 3 insertions, 2 deletions

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index a04756a26fe2..9c7fae08291d 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -307,9 +307,10 @@ static void update_spte(u64 *sptep, u64 new_spte)
 {
         u64 old_spte;
 
-        if (!shadow_accessed_mask || (new_spte & shadow_accessed_mask)) {
+        if (!shadow_accessed_mask || (new_spte & shadow_accessed_mask) ||
+              !is_rmap_spte(*sptep))
                 __set_spte(sptep, new_spte);
-        } else {
+        else {
                 old_spte = __xchg_spte(sptep, new_spte);
                 if (old_spte & shadow_accessed_mask)
                         mark_page_accessed(pfn_to_page(spte_to_pfn(old_spte)));