KVM: Remove redundant smp_mb() in the kvm_mmu_commit_zap_page()

There is already a barrier inside of kvm_flush_remote_tlbs() which can
help to make sure everyone sees our modifications to the page tables and
see changes to vcpu->mode here. So remove the smp_mb in the
kvm_mmu_commit_zap_page() and update the comment.

Signed-off-by: Lan Tianyu <tianyu.lan@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index e46a81f..fc8ab1f 100644 (file)
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -2390,14 +2390,13 @@ static void kvm_mmu_commit_zap_page(struct kvm *kvm,
                return;
 
        /*
-        * wmb: make sure everyone sees our modifications to the page tables
-        * rmb: make sure we see changes to vcpu->mode
-        */
-       smp_mb();
-
-       /*
-        * Wait for all vcpus to exit guest mode and/or lockless shadow
-        * page table walks.
+        * We need to make sure everyone sees our modifications to
+        * the page tables and see changes to vcpu->mode here. The barrier
+        * in the kvm_flush_remote_tlbs() achieves this. This pairs
+        * with vcpu_enter_guest and walk_shadow_page_lockless_begin/end.
+        *
+        * In addition, kvm_flush_remote_tlbs waits for all vcpus to exit
+        * guest mode and/or lockless shadow page table walks.
         */
        kvm_flush_remote_tlbs(kvm);