[PATCH v3 6/6] KVM: MMU: delay flush all tlbs on sync_page path

[Xiao Guangrong]

Quote from Avi:
| I don't think we need to flush immediately; set a "tlb dirty" bit somewhere
| that is cleareded when we flush the tlb.  kvm_mmu_notifier_invalidate_page()
| can consult the bit and force a flush if set. 

Signed-off-by: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxx>
---
 arch/x86/kvm/paging_tmpl.h |    4 ++--
 include/linux/kvm_host.h   |    7 +++++++
 virt/kvm/kvm_main.c        |    8 +++++++-
 3 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index dfb906f..d5c302a 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -781,14 +781,14 @@ static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
 		gfn = gpte_to_gfn(gpte);
 
 		if (FNAME(map_invalid_gpte)(vcpu, sp, &sp->spt[i], gpte)) {
-			kvm_flush_remote_tlbs(vcpu->kvm);
+			kvm_mark_tlbs_dirty(vcpu->kvm);
 			continue;
 		}
 
 		if (gfn != sp->gfns[i]) {
 			drop_spte(vcpu->kvm, &sp->spt[i],
 				      shadow_trap_nonpresent_pte);
-			kvm_flush_remote_tlbs(vcpu->kvm);
+			kvm_mark_tlbs_dirty(vcpu->kvm);
 			continue;
 		}
 
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 4bd663d..82d449b 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -249,6 +249,7 @@ struct kvm {
 	struct mmu_notifier mmu_notifier;
 	unsigned long mmu_notifier_seq;
 	long mmu_notifier_count;
+	atomic_t tlbs_dirty;
 #endif
 };
 
@@ -377,6 +378,12 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *vcpu);
 void kvm_resched(struct kvm_vcpu *vcpu);
 void kvm_load_guest_fpu(struct kvm_vcpu *vcpu);
 void kvm_put_guest_fpu(struct kvm_vcpu *vcpu);
+
+static inline void kvm_mark_tlbs_dirty(struct kvm *kvm)
+{
+	atomic_inc(&kvm->tlbs_dirty);
+}
+
 void kvm_flush_remote_tlbs(struct kvm *kvm);
 void kvm_reload_remote_mmus(struct kvm *kvm);
 
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index fb93ff9..2962569 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -168,8 +168,12 @@ static bool make_all_cpus_request(struct kvm *kvm, unsigned int req)
 
 void kvm_flush_remote_tlbs(struct kvm *kvm)
 {
+	int dirty_count = atomic_read(&kvm->tlbs_dirty);
+
+	smp_mb();
 	if (make_all_cpus_request(kvm, KVM_REQ_TLB_FLUSH))
 		++kvm->stat.remote_tlb_flush;
+	atomic_sub(dirty_count, &kvm->tlbs_dirty);
 }
 
 void kvm_reload_remote_mmus(struct kvm *kvm)
@@ -249,7 +253,8 @@ static void kvm_mmu_notifier_invalidate_page(struct mmu_notifier *mn,
 	idx = srcu_read_lock(&kvm->srcu);
 	spin_lock(&kvm->mmu_lock);
 	kvm->mmu_notifier_seq++;
-	need_tlb_flush = kvm_unmap_hva(kvm, address);
+	need_tlb_flush = kvm_unmap_hva(kvm, address) |
+			      atomic_read(&kvm->tlbs_dirty);
 	spin_unlock(&kvm->mmu_lock);
 	srcu_read_unlock(&kvm->srcu, idx);
 
@@ -293,6 +298,7 @@ static void kvm_mmu_notifier_invalidate_range_start(struct mmu_notifier *mn,
 	kvm->mmu_notifier_count++;
 	for (; start < end; start += PAGE_SIZE)
 		need_tlb_flush |= kvm_unmap_hva(kvm, start);
+	need_tlb_flush |= atomic_read(&kvm->tlbs_dirty);
 	spin_unlock(&kvm->mmu_lock);
 	srcu_read_unlock(&kvm->srcu, idx);
 
-- 
1.7.0.4

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