linux-kernel - Re: [PATCH v4 4/5] KVM: MMU: Add support for PKS emulation

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Message-ID: <YQLkczVfCsFp4IxW@google.com>
Date:   Thu, 29 Jul 2021 17:25:07 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Chenyi Qiang <chenyi.qiang@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.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>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 4/5] KVM: MMU: Add support for PKS emulation

On Fri, Feb 05, 2021, Chenyi Qiang wrote:
> In addition to the pkey check for user pages, advertise pkr_mask also to
> cache the conditions where protection key checks for supervisor pages
> are needed. Add CR4_PKS in mmu_role_bits to track the pkr_mask update on
> a per-mmu basis.
> 
> In original cache conditions of pkr_mask, U/S bit in page tables is a
> judgement condition and replace the PFEC.RSVD in page fault error code
> to form the index of 16 domains. PKS support would extend the U/S bits
> (if U/S=0, PKS check required). It adds an additional check for
> cr4_pke/cr4_pks to ensure the necessity and distinguish PKU and PKS from
> each other.
> 
> Signed-off-by: Chenyi Qiang <chenyi.qiang@...el.com>
> ---
>  arch/x86/include/asm/kvm_host.h | 11 +++---
>  arch/x86/kvm/mmu.h              | 13 ++++---
>  arch/x86/kvm/mmu/mmu.c          | 63 +++++++++++++++++++--------------
>  arch/x86/kvm/x86.c              |  3 +-
>  4 files changed, 53 insertions(+), 37 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 1909d34cbac8..e515f1cecb88 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -294,7 +294,7 @@ union kvm_mmu_extended_role {
>  		unsigned int cr0_pg:1;
>  		unsigned int cr4_pae:1;
>  		unsigned int cr4_pse:1;
> -		unsigned int cr4_pke:1;
> +		unsigned int cr4_pkr:1;

Smushing these together will not work, as this code (from below)

> -     ext.cr4_pke = !!kvm_read_cr4_bits(vcpu, X86_CR4_PKE);
> +     ext.cr4_pkr = !!kvm_read_cr4_bits(vcpu, X86_CR4_PKE) ||
> +                   !!kvm_read_cr4_bits(vcpu, X86_CR4_PKS);

will generate the same mmu_role for CR4.PKE=0,PKS=1 and CR4.PKE=1,PKS=1 (and
other combinations).  I.e. KVM will fail to reconfigure the MMU and thus skip
update_pkr_bitmask() if the guest toggles PKE or PKS while the other PK* bit is set.

>  		unsigned int cr4_smap:1;
>  		unsigned int cr4_smep:1;
>  		unsigned int maxphyaddr:6;