linux-kernel - Re: [PATCH v2 2/2] KVM: VMX: Fix VPID capability detection

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Date:   Tue, 17 Oct 2017 19:48:09 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Jim Mattson <jmattson@...gle.com>, Wanpeng Li <kernellwp@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        kvm list <kvm@...r.kernel.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>
Subject: Re: [PATCH v2 2/2] KVM: VMX: Fix VPID capability detection

On 17/10/2017 19:43, Jim Mattson wrote:
>> +               &vmx_capability.ept, &vmx_capability.vpid);
>> +
>>         if (_cpu_based_2nd_exec_control & SECONDARY_EXEC_ENABLE_EPT) {
>>                 /* CR3 accesses and invlpg don't need to cause VM Exits when EPT
>>                    enabled */
>>                 _cpu_based_exec_control &= ~(CPU_BASED_CR3_LOAD_EXITING |
>>                                              CPU_BASED_CR3_STORE_EXITING |
>>                                              CPU_BASED_INVLPG_EXITING);
>> -               rdmsr(MSR_IA32_VMX_EPT_VPID_CAP,
>> -                     vmx_capability.ept, vmx_capability.vpid);
>> -       }
>> +       } else
>> +               vmx_capability.ept = 0;
> I would expect vmx_capability.ept to already be 0 here. Otherwise, L0
> is reporting inconsistent VMX capabilities.
> 
>> +       if (!(_cpu_based_2nd_exec_control & SECONDARY_EXEC_ENABLE_VPID))
>> +               vmx_capability.vpid = 0;
> I would expect vmx_capability.vpid to already be 0 here. Otherwise, L0
> is reporting inconsistent VMX capabilities.
> 

That's true, but I think it's better to be safe.  Maybe add a pr_warn if
it is not zero?

Paolo