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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id by1sm158365ejc.30.2021.06.23.10.11.57 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 23 Jun 2021 10:11:58 -0700 (PDT) Subject: Re: [PATCH 16/54] KVM: x86/mmu: Drop smep_andnot_wp check from "uses NX" for shadow MMUs To: Sean Christopherson Cc: Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Yu Zhang , Maxim Levitsky References: <20210622175739.3610207-1-seanjc@google.com> <20210622175739.3610207-17-seanjc@google.com> From: Paolo Bonzini Message-ID: Date: Wed, 23 Jun 2021 19:11:57 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 MIME-Version: 1.0 In-Reply-To: <20210622175739.3610207-17-seanjc@google.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 22/06/21 19:57, Sean Christopherson wrote: > Drop the smep_andnot_wp role check from the "uses NX" calculation now > that all non-nested shadow MMUs treat NX as used via the !TDP check. > > The shadow MMU for nested NPT, which shares the helper, does not need to > deal with SMEP (or WP) as NPT walks are always "user" accesses and WP is > explicitly noted as being ignored: > > Table walks for guest page tables are always treated as user writes at > the nested page table level. > > A table walk for the guest page itself is always treated as a user > access at the nested page table level > > The host hCR0.WP bit is ignored under nested paging. > > Signed-off-by: Sean Christopherson > --- > arch/x86/kvm/mmu/mmu.c | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index 96c16a6e0044..ca7680d1ea24 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -4223,8 +4223,7 @@ reset_shadow_zero_bits_mask(struct kvm_vcpu *vcpu, struct kvm_mmu *context) > * NX can be used by any non-nested shadow MMU to avoid having to reset > * MMU contexts. Note, KVM forces EFER.NX=1 when TDP is disabled. > */ > - bool uses_nx = context->nx || !tdp_enabled || > - context->mmu_role.base.smep_andnot_wp; > + bool uses_nx = context->nx || !tdp_enabled; > struct rsvd_bits_validate *shadow_zero_check; > int i; > > Good idea, but why not squash it into patch 2? Paolo