Optimize TLB flush in kvm_mmu_slot_remove_write_access.

No TLB flush is needed when there's no valid rmap in memory slot.

Signed-off-by: Kai Huang <kai.huang@linux.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 0d0fdd6f002cc0bc115a0625891655cbe0c0563f..97898abe8386e188201a82da8b2d4cecee997c54 100644 (file)
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -4302,6 +4302,7 @@ void kvm_mmu_slot_remove_write_access(struct kvm *kvm, int slot)
        struct kvm_memory_slot *memslot;
        gfn_t last_gfn;
        int i;
+       bool flush = false;
 
        memslot = id_to_memslot(kvm->memslots, slot);
        last_gfn = memslot->base_gfn + memslot->npages - 1;
@@ -4318,7 +4319,8 @@ void kvm_mmu_slot_remove_write_access(struct kvm *kvm, int slot)
 
                for (index = 0; index <= last_index; ++index, ++rmapp) {
                        if (*rmapp)
-                               __rmap_write_protect(kvm, rmapp, false);
+                               flush |= __rmap_write_protect(kvm, rmapp,
+                                               false);
 
                        if (need_resched() || spin_needbreak(&kvm->mmu_lock))
                                cond_resched_lock(&kvm->mmu_lock);
@@ -4345,7 +4347,8 @@ void kvm_mmu_slot_remove_write_access(struct kvm *kvm, int slot)
         * instead of PT_WRITABLE_MASK, that means it does not depend
         * on PT_WRITABLE_MASK anymore.
         */
-       kvm_flush_remote_tlbs(kvm);
+       if (flush)
+               kvm_flush_remote_tlbs(kvm);
 }
 
 #define BATCH_ZAP_PAGES        10