linux-kernel - [PATCH 2/2] KVM: MMU: optimize pte write path if don't have protected sp

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Date:	Mon, 28 Mar 2011 10:30:42 +0800
From:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To:	Avi Kivity <avi@...hat.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: [PATCH 2/2] KVM: MMU: optimize pte write path if don't have protected
 sp

Simplely return from kvm_mmu_pte_write path if no shadow page is
write-protected, than we can avoid to walk all shadow pages and hold
mmu-lock

Signed-off-by: Xiao Guangrong <xiaoguangrong@...fujitsu.com>
---
 arch/x86/kvm/mmu.c |    8 ++++++++
 1 files changed, 8 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 2841805..ccac6c4 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -3219,6 +3219,11 @@ static void kvm_mmu_access_page(struct kvm_vcpu *vcpu, gfn_t gfn)
 		set_bit(PT_ACCESSED_SHIFT, (unsigned long *)spte);
 }
 
+static bool need_track_pte_changed(struct kvm_vcpu *vcpu)
+{
+	return !tdp_enabled || mmu_is_nested(vcpu);
+}
+
 void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
 		       const u8 *new, int bytes,
 		       bool guest_initiated)
@@ -3233,6 +3238,9 @@ 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 (!need_track_pte_changed(vcpu))
+		return;
+
 	zap_page = remote_flush = local_flush = false;
 	offset = offset_in_page(gpa);
 
-- 
1.7.4

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