linux-kernel - [PATCH 3.12 069/124] KVM: nSVM: Check for NRIPS support before updating control field

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Message-Id: <c441e7259d637ba9b3bebdfa32e1a6f0a13b06d2.1438076484.git.jslaby@suse.cz>
Date:	Tue, 28 Jul 2015 11:43:23 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, Bandan Das <bsd@...hat.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 069/124] KVM: nSVM: Check for NRIPS support before updating control field

From: Bandan Das <bsd@...hat.com>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit f104765b4f81fd74d69e0eb161e89096deade2db upstream.

If hardware doesn't support DecodeAssist - a feature that provides
more information about the intercept in the VMCB, KVM decodes the
instruction and then updates the next_rip vmcb control field.
However, NRIP support itself depends on cpuid Fn8000_000A_EDX[NRIPS].
Since skip_emulated_instruction() doesn't verify nrip support
before accepting control.next_rip as valid, avoid writing this
field if support isn't present.

Signed-off-by: Bandan Das <bsd@...hat.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 arch/x86/kvm/svm.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 5dcdff58b679..2996635196d3 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -495,8 +495,10 @@ static void skip_emulated_instruction(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
 
-	if (svm->vmcb->control.next_rip != 0)
+	if (svm->vmcb->control.next_rip != 0) {
+		WARN_ON(!static_cpu_has(X86_FEATURE_NRIPS));
 		svm->next_rip = svm->vmcb->control.next_rip;
+	}
 
 	if (!svm->next_rip) {
 		if (emulate_instruction(vcpu, EMULTYPE_SKIP) !=
@@ -4237,7 +4239,9 @@ static int svm_check_intercept(struct kvm_vcpu *vcpu,
 		break;
 	}
 
-	vmcb->control.next_rip  = info->next_rip;
+	/* TODO: Advertise NRIPS to guest hypervisor unconditionally */
+	if (static_cpu_has(X86_FEATURE_NRIPS))
+		vmcb->control.next_rip  = info->next_rip;
 	vmcb->control.exit_code = icpt_info.exit_code;
 	vmexit = nested_svm_exit_handled(svm);
 
-- 
2.4.6

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