linux-kernel - [PATCH 3.16.y-ckt 081/104] Use WARN_ON_ONCE for missing X86_FEATURE

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Message-Id: <1445867006-18048-82-git-send-email-luis.henriques@canonical.com>
Date:	Mon, 26 Oct 2015 13:43:03 +0000
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Dirk Mueller <dmueller@...e.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 081/104] Use WARN_ON_ONCE for missing X86_FEATURE_NRIPS

3.16.7-ckt19 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: =?UTF-8?q?Dirk=20M=C3=BCller?= <dmueller@...e.com>

commit d2922422c48df93f3edff7d872ee4f3191fefb08 upstream.

The cpu feature flags are not ever going to change, so warning
everytime can cause a lot of kernel log spam
(in our case more than 10GB/hour).

The warning seems to only occur when nested virtualization is
enabled, so it's probably triggered by a KVM bug.  This is a
sensible and safe change anyway, and the KVM bug fix might not
be suitable for stable releases anyway.

Signed-off-by: Dirk Mueller <dmueller@...e.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 arch/x86/kvm/svm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 37e85d0a1940..539f233965f1 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -512,7 +512,7 @@ static void skip_emulated_instruction(struct kvm_vcpu *vcpu)
 	struct vcpu_svm *svm = to_svm(vcpu);
 
 	if (svm->vmcb->control.next_rip != 0) {
-		WARN_ON(!static_cpu_has(X86_FEATURE_NRIPS));
+		WARN_ON_ONCE(!static_cpu_has(X86_FEATURE_NRIPS));
 		svm->next_rip = svm->vmcb->control.next_rip;
 	}
 
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