linux-kernel - Re: [RFC 5/7] KVM: MMU: Add support for PKS emulation

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Message-ID: <ed72302d-2644-75d4-f219-7855cf0430df@redhat.com>
Date:   Wed, 27 Jan 2021 09:37:12 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Chenyi Qiang <chenyi.qiang@...el.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Xiaoyao Li <xiaoyao.li@...el.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC 5/7] KVM: MMU: Add support for PKS emulation

On 27/01/21 04:00, Chenyi Qiang wrote:
>>
>>>
>>>          if (pte_access & PT_USER_MASK)
>>>              pkr_bits = (vcpu->arch.pkru >> (pte_pkey * 2)) & 3;
>>> +        else if (!kvm_get_msr(vcpu, MSR_IA32_PKRS, &pkrs))
>>> +            pkr_bits = (pkrs >> (pte_pkey * 2)) & 3;
>>
>> You should be able to always use vcpu->arch.pkrs here.  So
>>
>> pkr = pte_access & PT_USER_MASK ? vcpu->arch.pkru : vcpu->arch.pkrs;
>> pkr_bits = (pkr >> pte_pkey * 2) & 3;
>>
> Concerning vcpu->arch.pkrs would be the only use case in current 
> submitted patches, is it still necessary to shadow it?

Yes, please do.  kvm_get_msr is pretty slow, and the code becomes 
simpler too.

Paolo