linux-kernel - [PATCH v2 06/12] KVM: MMU: introduce a static table to map guest access to spte access

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Date:	Wed, 23 Jan 2013 18:07:20 +0800
From:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
To:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	Avi Kivity <avi.kivity@...il.com>,
	Gleb Natapov <gleb@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: [PATCH v2 06/12] KVM: MMU: introduce a static table to map guest
 access to spte access

It makes set_spte more clean and reduces branch prediction

Signed-off-by: Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
---
 arch/x86/kvm/mmu.c |   37 ++++++++++++++++++++++++++-----------
 1 files changed, 26 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 43b7e0c..a8a9c0e 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -235,6 +235,29 @@ static inline u64 rsvd_bits(int s, int e)
 	return ((1ULL << (e - s + 1)) - 1) << s;
 }

+static u64 gaccess_to_spte_access[ACC_ALL + 1];
+static void build_access_table(void)
+{
+	int access;
+
+	for (access = 0; access < ACC_ALL + 1; access++) {
+		u64 spte_access = 0;
+
+		if (access & ACC_EXEC_MASK)
+			spte_access |= shadow_x_mask;
+		else
+			spte_access |= shadow_nx_mask;
+
+		if (access & ACC_USER_MASK)
+			spte_access |= shadow_user_mask;
+
+		if (access & ACC_WRITE_MASK)
+			spte_access |= PT_WRITABLE_MASK | SPTE_MMU_WRITEABLE;
+
+		gaccess_to_spte_access[access] = spte_access;
+	}
+}
+
 void kvm_mmu_set_mask_ptes(u64 user_mask, u64 accessed_mask,
 		u64 dirty_mask, u64 nx_mask, u64 x_mask)
 {
@@ -243,6 +266,7 @@ void kvm_mmu_set_mask_ptes(u64 user_mask, u64 accessed_mask,
 	shadow_dirty_mask = dirty_mask;
 	shadow_nx_mask = nx_mask;
 	shadow_x_mask = x_mask;
+	build_access_table();
 }
 EXPORT_SYMBOL_GPL(kvm_mmu_set_mask_ptes);

@@ -2391,20 +2415,11 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
 	if (!speculative)
 		spte |= shadow_accessed_mask;

-	if (pte_access & ACC_EXEC_MASK)
-		spte |= shadow_x_mask;
-	else
-		spte |= shadow_nx_mask;
-
-	if (pte_access & ACC_USER_MASK)
-		spte |= shadow_user_mask;
-
-	if (pte_access & ACC_WRITE_MASK)
-		spte |= PT_WRITABLE_MASK | SPTE_MMU_WRITEABLE;
-
 	if (level > PT_PAGE_TABLE_LEVEL)
 		spte |= PT_PAGE_SIZE_MASK;

+	spte |= gaccess_to_spte_access[pte_access];
+
 	if (tdp_enabled)
 		spte |= kvm_x86_ops->get_mt_mask(vcpu, gfn,
 			kvm_is_mmio_pfn(pfn));
-- 
1.7.7.6

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