From: Peter Feiner <pfei...@google.com>
Optimization for avoiding lookups in mmu_page_hash. When there's a
single direct root, a shadow page has at most one parent SPTE
(non-root SPs have exactly one; the root has none). Thus, if an SPTE
is non-present, it can be linked to a newly allocated SP without
first checking if the SP already exists.
This optimization has proven significant in batch large SP shattering
where the hash lookup accounted for 95% of the overhead.
Signed-off-by: Peter Feiner <pfei...@google.com>
Signed-off-by: Jon Cargille <jcarg...@google.com>
Reviewed-by: Jim Mattson <jmatt...@google.com>
---
arch/x86/include/asm/kvm_host.h | 13 ++++++++
arch/x86/kvm/mmu/mmu.c | 55 +++++++++++++++++++--------------
2 files changed, 45 insertions(+), 23 deletions(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index a239a297be33..9b70d764b626 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -913,6 +913,19 @@ struct kvm_arch {
struct kvm_page_track_notifier_node mmu_sp_tracker;
struct kvm_page_track_notifier_head track_notifier_head;
+ /*
+ * Optimization for avoiding lookups in mmu_page_hash. When there's a
+ * single direct root, a shadow page has at most one parent SPTE
+ * (non-root SPs have exactly one; the root has none). Thus, if an SPTE
+ * is non-present, it can be linked to a newly allocated SP without
+ * first checking if the SP already exists.
+ *
+ * False initially because there are no indirect roots.
+ *
+ * Guarded by mmu_lock.
+ */
+ bool shadow_page_may_have_multiple_parents;
+
struct list_head assigned_dev_head;
struct iommu_domain *iommu_domain;
bool iommu_noncoherent;
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index e618472c572b..d94552b0ed77 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -2499,35 +2499,40 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct
kvm_vcpu *vcpu,
quadrant &= (1 << ((PT32_PT_BITS - PT64_PT_BITS) * level)) - 1;
role.quadrant = quadrant;
}
- for_each_valid_sp(vcpu->kvm, sp, gfn) {
- if (sp->gfn != gfn) {
- collisions++;
- continue;
- }
- if (!need_sync && sp->unsync)
- need_sync = true;
+ if (vcpu->kvm->arch.shadow_page_may_have_multiple_parents ||
+ level == vcpu->arch.mmu->root_level) {
+ for_each_valid_sp(vcpu->kvm, sp, gfn) {
+ if (sp->gfn != gfn) {
+ collisions++;
+ continue;
+ }
- if (sp->role.word != role.word)
- continue;
+ if (!need_sync && sp->unsync)
+ need_sync = true;
- if (sp->unsync) {
- /* The page is good, but __kvm_sync_page might still end
- * up zapping it. If so, break in order to rebuild it.
- */
- if (!__kvm_sync_page(vcpu, sp, &invalid_list))
- break;
+ if (sp->role.word != role.word)
+ continue;
- WARN_ON(!list_empty(&invalid_list));
- kvm_make_request(KVM_REQ_TLB_FLUSH_CURRENT, vcpu);
- }
+ if (sp->unsync) {
+ /* The page is good, but __kvm_sync_page might
+ * still end up zapping it. If so, break in
+ * order to rebuild it.
+ */
+ if (!__kvm_sync_page(vcpu, sp, &invalid_list))
+ break;
- if (sp->unsync_children)
- kvm_make_request(KVM_REQ_TLB_FLUSH_CURRENT, vcpu);
+ WARN_ON(!list_empty(&invalid_list));
+ kvm_make_request(KVM_REQ_TLB_FLUSH_CURRENT,
vcpu);
+ }
- __clear_sp_write_flooding_count(sp);
- trace_kvm_mmu_get_page(sp, false);
- goto out;
+ if (sp->unsync_children)
+ kvm_make_request(KVM_REQ_TLB_FLUSH_CURRENT,
vcpu);
+
+ __clear_sp_write_flooding_count(sp);
+ trace_kvm_mmu_get_page(sp, false);
+ goto out;
+ }
}
++vcpu->kvm->stat.mmu_cache_miss;
@@ -3735,6 +3740,10 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu)
gfn_t root_gfn, root_pgd;
int i;
+ spin_lock(&vcpu->kvm->mmu_lock);
+ vcpu->kvm->arch.shadow_page_may_have_multiple_parents = true;
+ spin_unlock(&vcpu->kvm->mmu_lock);
+
root_pgd = vcpu->arch.mmu->get_guest_pgd(vcpu);
root_gfn = root_pgd >> PAGE_SHIFT;
--
2.26.2.303.gf8c07b1a785-goog
