linux-kernel - [PATCH v2 6/6] KVM: MMU: using __xchg

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Date:	Fri, 16 Jul 2010 11:30:18 +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 list <kvm@...r.kernel.org>
Subject: [PATCH v2 6/6] KVM: MMU: using __xchg_spte more smarter

Sometimes, atomically set spte is not needed, this patch call __xchg_spte()
more smartly

Note: if the old mapping's access bit is already set, we no need atomic operation
since the access bit is not lost

Signed-off-by: Xiao Guangrong <xiaoguangrong@...fujitsu.com>
---
 arch/x86/kvm/mmu.c |    9 +++++++--
 1 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index fb3ae54..71e9268 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -682,9 +682,14 @@ static void rmap_remove(struct kvm *kvm, u64 *spte)
 static void set_spte_track_bits(u64 *sptep, u64 new_spte)
 {
 	pfn_t pfn;
-	u64 old_spte;
+	u64 old_spte = *sptep;
+
+	if (!shadow_accessed_mask || !is_shadow_present_pte(old_spte) ||
+	      old_spte & shadow_accessed_mask) {
+		__set_spte(sptep, new_spte);
+	} else
+		old_spte = __xchg_spte(sptep, new_spte);
 
-	old_spte = __xchg_spte(sptep, new_spte);
 	if (!is_rmap_spte(old_spte))
 		return;
 	pfn = spte_to_pfn(old_spte);
-- 
1.6.1.2


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