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>

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 7ce92f7..58c35de 100644 (file)
--- 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)