linux-kernel - Re: [PATCH RESEND v12 00/17] KVM: x86/pmu: Add basic support to enable guest PEBS via DS

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Date:   Wed, 25 May 2022 17:12:26 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Like Xu <like.xu.linux@...il.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, Jim Mattson <jmattson@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
Subject: Re: [PATCH RESEND v12 00/17] KVM: x86/pmu: Add basic support to
 enable guest PEBS via DS

On Wed, 2022-05-25 at 16:32 +0800, Like Xu wrote:
> On 25/5/2022 4:14 pm, Paolo Bonzini wrote:
> > On 5/25/22 09:56, Like Xu wrote:
> > > Thanks for the clarification.
> > > 
> > > Some kvm x86 selftests have been failing due to this issue even after the last 
> > > commit.
> > > 
> > > I blame myself for not passing the msr_info->host_initiated to the 
> > > intel_is_valid_msr(),
> > > meanwhile I pondered further whether we should check only the MSR addrs range in
> > > the kvm_pmu_is_valid_msr() and apply this kind of sanity check in the 
> > > pmu_set/get_msr().
> > > 
> > > Vitaly && Paolo, any preference to move forward ?
> > 
> > I'm not sure what I did wrong to not see the failure, so I'll fix it myself.
> 
> More info, some Skylake hosts fail the tests like x86_64/state_test due to this 
> issue.
> 
> > But from now on, I'll have a hard rule of no new processor features enabled 
> > without KVM unit tests or selftests.  In fact, it would be nice if you wrote 
> > some for PEBS.
> 
> Great, my team (or at least me) is committed to contributing more tests on vPMU 
> features.
> 
> We may update the process document to the 
> Documentation/virt/kvm/review-checklist.rst.
> 
> > Paolo
> > 

FYI, this patch series also break 'msr' test in kvm-unit tests.
(kvm/queue of today, and master of the kvm-unit-tests repo)

The test tries to set the MSR_IA32_MISC_ENABLE to 0x400c51889 and gets #GP.


Commenting this out, gets rid of #GP, but test still fails with unexpected result

		if (!msr_info->host_initiated &&
		    ((old_val ^ data) & MSR_IA32_MISC_ENABLE_PEBS_UNAVAIL))
			return 1;




It is very possible that the test is broken, I'll check this later.

Best regards,
	Maxim Levitsky