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From: Joerg Roedel <joro@8bytes.org>
To: Bandan Das <bsd@redhat.com>
Cc: "Paolo Bonzini" <pbonzini@redhat.com>,
	kvm@vger.kernel.org, "Dirk Müller" <dmueller@suse.com>
Subject: Re: [PATCH] Use WARN_ON_ONCE for missing X86_FEATURE_NRIPS
Date: Tue, 6 Oct 2015 12:28:38 +0200	[thread overview]
Message-ID: <20151006102838.GD20886@8bytes.org> (raw)
In-Reply-To: <jpgbncixlts.fsf@linux.bootlegged.copy>

On Thu, Oct 01, 2015 at 06:31:27PM -0400, Bandan Das wrote:
> >> @@ -514,7 +514,7 @@ 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;
> >>  	}

I looked again how this could possibly be triggered, and I am somewhat
confused now.

So svm->vmcb->control.next_rip is only written by hardware or in
svm_check_intercept(). Both cases write only to this field, if the
hardware supports X86_FEATURE_NRIPS. The write in nested_svm_vmexit only
targets the guests VMCB, and we don't use that one again.

So I can't see how the WARN_ON above could be triggered. Do I miss
something or might this also be a miscompilation of static_cpu_has?


	Joerg


  parent reply	other threads:[~2015-10-06 10:28 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-10-01 11:43 [PATCH] Use WARN_ON_ONCE for missing X86_FEATURE_NRIPS Dirk Müller
2015-10-01 12:25 ` Paolo Bonzini
2015-10-01 12:45   ` Dirk Müller
2015-10-01 12:31 ` Paolo Bonzini
2015-10-01 22:31   ` Bandan Das
2015-10-02  6:43     ` Dirk Müller
2015-10-05  1:15       ` Bandan Das
2015-10-05  9:50     ` Joerg Roedel
2015-10-05 16:54       ` Bandan Das
2015-10-05 17:15         ` Joerg Roedel
2015-10-05 17:42           ` Bandan Das
2015-10-06 10:23             ` Joerg Roedel
2015-10-06 18:02               ` Bandan Das
2015-10-05 20:12           ` Dirk Müller
2015-10-05 22:00             ` Bandan Das
2015-10-06 10:28     ` Joerg Roedel [this message]
2015-10-06 17:59       ` Bandan Das
2015-10-07 11:03         ` Joerg Roedel
2015-10-07 12:47           ` [PATCH] kvm: svm: Only propagate next_rip when guest supports it Joerg Roedel
2015-10-07 12:57             ` kbuild test robot
2015-10-07 15:48             ` Bandan Das
2015-10-07 16:14               ` Joerg Roedel
2015-10-07 17:03                 ` Dirk Müller
2015-10-07 14:58           ` [PATCH] Use WARN_ON_ONCE for missing X86_FEATURE_NRIPS Bandan Das
2015-10-07 15:24             ` Joerg Roedel

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