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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id s23sm10619916wmc.35.2021.02.26.01.38.53 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 26 Feb 2021 01:38:54 -0800 (PST) Subject: Re: [PATCH 00/24] KVM: x86/mmu: Introduce MMU_PRESENT and fix bugs To: Sean Christopherson Cc: Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Ben Gardon References: <20210225204749.1512652-1-seanjc@google.com> From: Paolo Bonzini Message-ID: Date: Fri, 26 Feb 2021 10:38:52 +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: <20210225204749.1512652-1-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 25/02/21 21:47, Sean Christopherson wrote: > This series adds the simple idea of tagging shadow-present SPTEs with > a single bit, instead of looking for non-zero SPTEs that aren't MMIO and > aren't REMOVED. Doing so reduces KVM's code footprint by 2k bytes on > x86-64, and presumably adds a tiny performance boost in related paths. > > But, actually adding MMU_PRESENT without breaking one flow or another is > a bit of a debacle. The main issue is that EPT doesn't have many low > available bits, and PAE doesn't have any high available bits. And, the > existing MMU_WRITABLE and HOST_WRITABLE flags aren't optional, i.e. are > needed for all flavors of paging. The solution I settled on is to let > make the *_WRITABLE bit configurable so that EPT can use high available > bits. > > Of course, I forgot the above PAE restriction multiple times, and > journeyed down several dead ends. The most notable failed idea was > using the AD_* masks in bits 52 and 53 to denote shadow-present SPTEs. > That would have been quite clever as it would provide the same benefits > without burning another available bit. > > Along the many failed attempts, I collected a variety of bug fixes and > cleanups, mostly things found by inspection after doing a deep dive to > figure out what I broke. > > Sean Christopherson (24): > KVM: x86/mmu: Set SPTE_AD_WRPROT_ONLY_MASK if and only if PML is > enabled > KVM: x86/mmu: Check for shadow-present SPTE before querying A/D status > KVM: x86/mmu: Bail from fast_page_fault() if SPTE is not > shadow-present > KVM: x86/mmu: Disable MMIO caching if MMIO value collides with L1TF > KVM: x86/mmu: Retry page faults that hit an invalid memslot > KVM: x86/mmu: Don't install bogus MMIO SPTEs if MMIO caching is > disabled > KVM: x86/mmu: Handle MMIO SPTEs directly in mmu_set_spte() > KVM: x86/mmu: Drop redundant trace_kvm_mmu_set_spte() in the TDP MMU > KVM: x86/mmu: Rename 'mask' to 'spte' in MMIO SPTE helpers > KVM: x86/mmu: Stop using software available bits to denote MMIO SPTEs > KVM: x86/mmu: Add module param to disable MMIO caching (for testing) > KVM: x86/mmu: Rename and document A/D scheme for TDP SPTEs > KVM: x86/mmu: Use MMIO SPTE bits 53 and 52 for the MMIO generation > KVM: x86/mmu: Document dependency bewteen TDP A/D type and saved bits > KVM: x86/mmu: Move initial kvm_mmu_set_mask_ptes() call into MMU > proper > KVM: x86/mmu: Co-locate code for setting various SPTE masks > KVM: x86/mmu: Move logic for setting SPTE masks for EPT into the MMU > proper > KVM: x86/mmu: Make Host-writable and MMU-writable bit locations > dynamic > KVM: x86/mmu: Use high bits for host/mmu writable masks for EPT SPTEs > KVM: x86/mmu: Use a dedicated bit to track shadow/MMU-present SPTEs > KVM: x86/mmu: Tweak auditing WARN for A/D bits to !PRESENT (was MMIO) > KVM: x86/mmu: Use is_removed_spte() instead of open coded equivalents > KVM: x86/mmu: Use low available bits for removed SPTEs > KVM: x86/mmu: Dump reserved bits if they're detected on non-MMIO SPTE > > Documentation/virt/kvm/locking.rst | 49 +++++---- > arch/x86/include/asm/kvm_host.h | 3 - > arch/x86/kvm/mmu.h | 15 +-- > arch/x86/kvm/mmu/mmu.c | 87 +++++++--------- > arch/x86/kvm/mmu/mmu_internal.h | 16 +-- > arch/x86/kvm/mmu/paging_tmpl.h | 2 +- > arch/x86/kvm/mmu/spte.c | 157 ++++++++++++++++++++--------- > arch/x86/kvm/mmu/spte.h | 135 +++++++++++++++++-------- > arch/x86/kvm/mmu/tdp_mmu.c | 22 ++-- > arch/x86/kvm/svm/svm.c | 2 +- > arch/x86/kvm/vmx/vmx.c | 24 +---- > arch/x86/kvm/x86.c | 3 - > 12 files changed, 290 insertions(+), 225 deletions(-) > Queued (patch 1 for 5.12, the rest for 5.13). Paolo