[PATCH] Optimize TLB flush in kvm_mmu_slot_remove_write_access.

[PATCH] Optimize TLB flush in kvm_mmu_slot_remove_write_access.

[Kai Huang]

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

Signed-off-by: Kai Huang <kai.huang@linux.intel.com>
---
 arch/x86/kvm/mmu.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index f83fc6c..d43bf50 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -4309,6 +4309,7 @@ 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;
@@ -4325,7 +4326,8 @@ 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);
@@ -4352,7 +4354,8 @@ 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
-- 
2.1.0