linux-kernel - Re: [RFC 4/7] KVM: MMU: Refactor pkr

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Date:   Wed, 27 Jan 2021 11:14:01 +0800
From:   Chenyi Qiang <chenyi.qiang@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.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 4/7] KVM: MMU: Refactor pkr_mask to cache condition



On 1/27/2021 2:16 AM, Paolo Bonzini wrote:
> On 07/08/20 10:48, Chenyi Qiang wrote:
>>
>>          * index of the protection domain, so pte_pkey * 2 is
>>          * is the index of the first bit for the domain.
>>          */
>> -        pkr_bits = (vcpu->arch.pkru >> (pte_pkey * 2)) & 3;
>> +        if (pte_access & PT_USER_MASK)
>> +            pkr_bits = (vcpu->arch.pkru >> (pte_pkey * 2)) & 3;
>> +        else
>> +            pkr_bits = 0;
>>
>> -        /* clear present bit, replace PFEC.RSVD with ACC_USER_MASK. */
>> -        offset = (pfec & ~1) +
>> -            ((pte_access & PT_USER_MASK) << (PFERR_RSVD_BIT - 
>> PT_USER_SHIFT));
>> +        /* clear present bit */
>> +        offset = (pfec & ~1);
>>
>>          pkr_bits &= mmu->pkr_mask >> offset;
>>          errcode |= -pkr_bits & PFERR_PK_MASK;
> 
> I think this is incorrect.  mmu->pkr_mask must cover both clear and set 
> ACC_USER_MASK, in to cover all combinations of CR4.PKE and CR4.PKS. 
> Right now, check_pkey is !ff && pte_user, but you need to make it 
> something like
> 
>      check_pkey = !ff && (pte_user ? cr4_pke : cr4_pks);
> 
> Paolo

Oh, I didn't distinguish the cr4_pke/cr4_pks check. Will fix this issue.

>