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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id n23sm579324wra.71.2021.03.05.09.44.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 05 Mar 2021 09:44:19 -0800 (PST) Subject: Re: [PATCH v2 11/17] KVM: x86/mmu: Mark the PAE roots as decrypted for shadow paging To: Sean Christopherson Cc: Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Ben Gardon , Brijesh Singh , Tom Lendacky References: <20210305011101.3597423-1-seanjc@google.com> <20210305011101.3597423-12-seanjc@google.com> From: Paolo Bonzini Message-ID: Date: Fri, 5 Mar 2021 18:44:18 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: <20210305011101.3597423-12-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: kvm@vger.kernel.org On 05/03/21 02:10, Sean Christopherson wrote: > @@ -5301,6 +5307,22 @@ static int __kvm_mmu_create(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu) > for (i = 0; i < 4; ++i) > mmu->pae_root[i] = 0; I think this should be deleted, since you have another identical for loop below? Paolo > + /* > + * CR3 is only 32 bits when PAE paging is used, thus it's impossible to > + * get the CPU to treat the PDPTEs as encrypted. Decrypt the page so > + * that KVM's writes and the CPU's reads get along. Note, this is > + * only necessary when using shadow paging, as 64-bit NPT can get at > + * the C-bit even when shadowing 32-bit NPT, and SME isn't supported > + * by 32-bit kernels (when KVM itself uses 32-bit NPT). > + */ > + if (!tdp_enabled) > + set_memory_decrypted((unsigned long)mmu->pae_root, 1); > + else > + WARN_ON_ONCE(shadow_me_mask); > + > + for (i = 0; i < 4; ++i) > + mmu->pae_root[i] = 0; > +