linux-kernel - Re: [PATCH 1/2] KVM: vmx, pmu: accept 0 for absent MSRs when host-initiated

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Message-ID: <4b59b1c0-112b-5e07-e613-607220c3b597@redhat.com>
Date:   Wed, 1 Jun 2022 10:54:11 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        likexu@...cent.com, Yang Weijiang <weijiang.yang@...el.com>
Subject: Re: [PATCH 1/2] KVM: vmx, pmu: accept 0 for absent MSRs when
 host-initiated

On 5/31/22 20:37, Sean Christopherson wrote:
>> +
>>   		/*
>>   		 * Writing depth MSR from guest could either setting the
>>   		 * MSR or resetting the LBR records with the side-effect.
>> @@ -535,6 +542,8 @@ static int intel_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>>   	case MSR_ARCH_LBR_CTL:
>>   		if (!arch_lbr_ctl_is_valid(vcpu, data))
>>   			break;
>> +		if (!guest_cpuid_has(vcpu, X86_FEATURE_ARCH_LBR))
>> +			return 0;
> 
> Similar bug here.
> 
> Can we just punt this out of kvm/queue until its been properly reviewed?

Yes, I agree.  I have started making some changes and pushed the result 
to kvm/arch-lbr-for-weijiang.

Most of the MSR handling is rewritten (and untested).

The nested VMX handling was also completely broken so I just removed it. 
  Instead, KVM should be adjusted so that it does not whine.

Paolo