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From:   Tianyu Lan <Tianyu.Lan@microsoft.com>
CC:     Tianyu Lan <Tianyu.Lan@microsoft.com>,
        "pbonzini@redhat.com" <pbonzini@redhat.com>,
        "rkrcmar@redhat.com" <rkrcmar@redhat.com>,
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        "hpa@zytor.com" <hpa@zytor.com>, "x86@kernel.org" <x86@kernel.org>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: [PATCH] KVM/X86: Check input sreg values before loading vcpu
Thread-Topic: [PATCH] KVM/X86: Check input sreg values before loading vcpu
Thread-Index: AQHTr5hN8NOqe9GuWkWmcSxT1Wc7aQ==
Date:   Tue, 27 Feb 2018 06:57:59 +0000
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From: Lan Tianyu <Tianyu.Lan@microsoft.com>

This patch is to check sreg value first and then load vcpu in order
to avoid redundant loading/putting vcpu.

Signed-off-by: Lan Tianyu <Tianyu.Lan@microsoft.com>
---
 arch/x86/kvm/x86.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c8a0b54..46da9ec 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7671,6 +7671,10 @@ EXPORT_SYMBOL_GPL(kvm_task_switch);
=20
 int kvm_valid_sregs(struct kvm_vcpu *vcpu, struct kvm_sregs *sregs)
 {
+	if (!guest_cpuid_has(vcpu, X86_FEATURE_XSAVE) &&
+			(sregs->cr4 & X86_CR4_OSXSAVE))
+		return -EINVAL;
+
 	if ((sregs->efer & EFER_LME) && (sregs->cr0 & X86_CR0_PG)) {
 		/*
 		 * When EFER.LME and CR0.PG are set, the processor is in
@@ -7701,14 +7705,10 @@ int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *=
vcpu,
 	struct desc_ptr dt;
 	int ret =3D -EINVAL;
=20
-	vcpu_load(vcpu);
-
-	if (!guest_cpuid_has(vcpu, X86_FEATURE_XSAVE) &&
-			(sregs->cr4 & X86_CR4_OSXSAVE))
-		goto out;
-
 	if (kvm_valid_sregs(vcpu, sregs))
-		goto out;
+		return ret;
+
+	vcpu_load(vcpu);
=20
 	apic_base_msr.data =3D sregs->apic_base;
 	apic_base_msr.host_initiated =3D true;
--=20
2.7.4