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

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Date:   Tue, 26 Jan 2021 19:16:13 +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 4/7] KVM: MMU: Refactor pkr_mask to cache condition

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