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([2001:b07:6468:f312:63a7:c72e:ea0e:6045]) by smtp.gmail.com with ESMTPSA id go10sm452325ejc.115.2021.11.10.14.44.55 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 10 Nov 2021 14:44:55 -0800 (PST) Message-ID: <80407e4a-36e1-e606-ed9f-74429f850e77@redhat.com> Date: Wed, 10 Nov 2021 23:44:54 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.2.0 Subject: Re: [RFC 11/19] KVM: x86/mmu: Factor shadow_zero_check out of make_spte Content-Language: en-US To: Ben Gardon , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: Peter Xu , Sean Christopherson , Peter Shier , David Matlack , Mingwei Zhang , Yulei Zhang , Wanpeng Li , Xiao Guangrong , Kai Huang , Keqian Zhu , David Hildenbrand References: <20211110223010.1392399-1-bgardon@google.com> <20211110223010.1392399-12-bgardon@google.com> From: Paolo Bonzini In-Reply-To: <20211110223010.1392399-12-bgardon@google.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/10/21 23:30, Ben Gardon wrote: > - WARN_ONCE(is_rsvd_spte(&vcpu->arch.mmu->shadow_zero_check, spte, level), > + WARN_ONCE(is_rsvd_spte(shadow_zero_check, spte, level), > "spte = 0x%llx, level = %d, rsvd bits = 0x%llx", spte, level, > - get_rsvd_bits(&vcpu->arch.mmu->shadow_zero_check, spte, level)); > + get_rsvd_bits(shadow_zero_check, spte, level)); Hmm, there is a deeper issue here, in that when using EPT/NPT (on either the legacy aka shadow or the TDP MMU) large parts of vcpu->arch.mmu are really the same for all vCPUs. The only thing that varies is those parts that actually depend on the guest's paging mode---the extended role, the reserved bits, etc. Those are needed by the emulator, but don't really belong in vcpu->arch.mmu when EPT/NPT is in use. I wonder if there's room for splitting kvm_mmu in two parts, such as kvm_mmu and kvm_guest_paging_context, and possibly change the walk_mmu pointer into a pointer to kvm_guest_paging_context. This way the EPT/NPT MMU (again either shadow or TDP) can be moved to kvm->arch. It should simplify this series and also David's work on eager page splitting. I'm not asking you to do this, of course, but perhaps I can trigger Sean's itch to refactor stuff. :) Paolo