KVM: MMU: collapse remote TLB flushes on root sync

Collapse remote TLB flushes on root sync.

kernbench is 2.7% faster on 4-way guest. Improvements have been seen
with other loads such as AIM7.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 14 insertions, 5 deletions

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 7ce92f78f337..58c35dead321 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -621,7 +621,7 @@ static u64 *rmap_next(struct kvm *kvm, unsigned long *rmapp, u64 *spte)
         return NULL;
 }
 
-static void rmap_write_protect(struct kvm *kvm, u64 gfn)
+static int rmap_write_protect(struct kvm *kvm, u64 gfn)
 {
         unsigned long *rmapp;
         u64 *spte;
@@ -667,8 +667,7 @@ static void rmap_write_protect(struct kvm *kvm, u64 gfn)
                 spte = rmap_next(kvm, rmapp, spte);
         }
 
-        if (write_protected)
-                kvm_flush_remote_tlbs(kvm);
+        return write_protected;
 }
 
 static int kvm_unmap_rmapp(struct kvm *kvm, unsigned long *rmapp)
@@ -1083,7 +1082,8 @@ static int kvm_sync_page(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
                 return 1;
         }
 
-        rmap_write_protect(vcpu->kvm, sp->gfn);
+        if (rmap_write_protect(vcpu->kvm, sp->gfn))
+                kvm_flush_remote_tlbs(vcpu->kvm);
         kvm_unlink_unsync_page(vcpu->kvm, sp);
         if (vcpu->arch.mmu.sync_page(vcpu, sp)) {
                 kvm_mmu_zap_page(vcpu->kvm, sp);
@@ -1162,6 +1162,14 @@ static void mmu_sync_children(struct kvm_vcpu *vcpu,
 
         kvm_mmu_pages_init(parent, &parents, &pages);
         while (mmu_unsync_walk(parent, &pages)) {
+                int protected = 0;
+
+                for_each_sp(pages, sp, parents, i)
+                        protected |= rmap_write_protect(vcpu->kvm, sp->gfn);
+
+                if (protected)
+                        kvm_flush_remote_tlbs(vcpu->kvm);
+
                 for_each_sp(pages, sp, parents, i) {
                         kvm_sync_page(vcpu, sp);
                         mmu_pages_clear_parents(&parents);
@@ -1226,7 +1234,8 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
         sp->role = role;
         hlist_add_head(&sp->hash_link, bucket);
         if (!metaphysical) {
-                rmap_write_protect(vcpu->kvm, gfn);
+                if (rmap_write_protect(vcpu->kvm, gfn))
+                        kvm_flush_remote_tlbs(vcpu->kvm);
                 account_shadowed(vcpu->kvm, gfn);
         }
         if (shadow_trap_nonpresent_pte != shadow_notrap_nonpresent_pte)