Patch "KVM: nSVM: Check for NRIPS support before updating control field" has been added to the 3.14-stable tree

This is a note to let you know that I've just added the patch titled

KVM: nSVM: Check for NRIPS support before updating control field

to the 3.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
kvm-nsvm-check-for-nrips-support-before-updating-control-field.patch
and it can be found in the queue-3.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Bandan Das <[email protected]>
Date: Thu, 11 Jun 2015 02:05:33 -0400
Subject: KVM: nSVM: Check for NRIPS support before updating control field

From: Bandan Das <[email protected]>

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.

---
 arch/x86/kvm/svm.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

@@ -495,8 +495,10 @@ static void skip_emulated_instruction(st
 {
 	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) !=

@@ -4246,7 +4248,9 @@ static int svm_check_intercept(struct kv
 		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);
 

Patches currently in stable-queue which might be from [email protected] are

queue-3.14/kvm-nsvm-check-for-nrips-support-before-updating-control-field.patch