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Subject[PATCH v2 1/7] KVM: MMU: optimize pte write path if don't have protected sp
Simply return from kvm_mmu_pte_write path if no shadow page is
write-protected, then we can avoid to walk all shadow pages and hold
mmu-lock

Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
---
arch/x86/include/asm/kvm_host.h | 1 +
arch/x86/kvm/mmu.c | 9 +++++++++
2 files changed, 10 insertions(+), 0 deletions(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index d2ac8e2..152601a 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -441,6 +441,7 @@ struct kvm_arch {
unsigned int n_used_mmu_pages;
unsigned int n_requested_mmu_pages;
unsigned int n_max_mmu_pages;
+ unsigned int indirect_shadow_pages;
atomic_t invlpg_counter;
struct hlist_head mmu_page_hash[KVM_NUM_MMU_PAGES];
/*
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 2841805..ad520d4 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -498,6 +498,7 @@ static void account_shadowed(struct kvm *kvm, gfn_t gfn)
linfo = lpage_info_slot(gfn, slot, i);
linfo->write_count += 1;
}
+ kvm->arch.indirect_shadow_pages++;
}

static void unaccount_shadowed(struct kvm *kvm, gfn_t gfn)
@@ -513,6 +514,7 @@ static void unaccount_shadowed(struct kvm *kvm, gfn_t gfn)
linfo->write_count -= 1;
WARN_ON(linfo->write_count < 0);
}
+ kvm->arch.indirect_shadow_pages--;
}

static int has_wrprotected_page(struct kvm *kvm,
@@ -3233,6 +3235,13 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
int level, npte, invlpg_counter, r, flooded = 0;
bool remote_flush, local_flush, zap_page;

+ /*
+ * If we don't have indirect shadow pages, it means no page is
+ * write-protected, so we can exit simply.
+ */
+ if (!ACCESS_ONCE(vcpu->kvm->arch.indirect_shadow_pages))
+ return;
+
zap_page = remote_flush = local_flush = false;
offset = offset_in_page(gpa);

--
1.7.4.4

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