linux-kernel - [PATCH] KVM: x86: optimize check for valid PAT value

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Date:   Wed, 10 Apr 2019 11:55:26 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: [PATCH] KVM: x86: optimize check for valid PAT value

This check will soon be done on every nested vmentry and vmexit,
"parallelize" it using bitwise operations.

Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 arch/x86/kvm/mtrr.c    | 10 +---------
 arch/x86/kvm/vmx/vmx.c |  2 +-
 arch/x86/kvm/x86.h     |  8 ++++++++
 3 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kvm/mtrr.c b/arch/x86/kvm/mtrr.c
index e9ea2d45ae66..9f72cc427158 100644
--- a/arch/x86/kvm/mtrr.c
+++ b/arch/x86/kvm/mtrr.c
@@ -48,11 +48,6 @@ static bool msr_mtrr_valid(unsigned msr)
 	return false;
 }
 
-static bool valid_pat_type(unsigned t)
-{
-	return t < 8 && (1 << t) & 0xf3; /* 0, 1, 4, 5, 6, 7 */
-}
-
 static bool valid_mtrr_type(unsigned t)
 {
 	return t < 8 && (1 << t) & 0x73; /* 0, 1, 4, 5, 6 */
@@ -67,10 +62,7 @@ bool kvm_mtrr_valid(struct kvm_vcpu *vcpu, u32 msr, u64 data)
 		return false;
 
 	if (msr == MSR_IA32_CR_PAT) {
-		for (i = 0; i < 8; i++)
-			if (!valid_pat_type((data >> (i * 8)) & 0xff))
-				return false;
-		return true;
+		return kvm_pat_valid(data);
 	} else if (msr == MSR_MTRRdefType) {
 		if (data & ~0xcff)
 			return false;
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index b6c533afbf27..b74679732cfc 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1891,7 +1891,7 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		break;
 	case MSR_IA32_CR_PAT:
 		if (vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_IA32_PAT) {
-			if (!kvm_mtrr_valid(vcpu, MSR_IA32_CR_PAT, data))
+			if (!kvm_pat_valid(data))
 				return 1;
 			vmcs_write64(GUEST_IA32_PAT, data);
 			vcpu->arch.pat = data;
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 28406aa1136d..7bc7ac9d2a44 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -347,4 +347,12 @@ static inline void kvm_after_interrupt(struct kvm_vcpu *vcpu)
 	__this_cpu_write(current_vcpu, NULL);
 }
 
+static inline bool kvm_pat_valid(u64 data)
+{
+	if (data & 0xF8F8F8F8F8F8F8F8)
+		return false;
+	/* 0, 1, 4, 5, 6, 7 are valid values.  */
+	return (data | ((data & 0x0202020202020202) << 1)) == data;
+}
+
 #endif
-- 
1.8.3.1