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([2001:b07:6468:f312:5e2c:eb9a:a8b6:fd3e]) by smtp.gmail.com with ESMTPSA id d3sm10226839wrr.2.2020.12.06.02.09.44 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 06 Dec 2020 02:09:45 -0800 (PST) Subject: Re: [PATCH] KVM: mmu: Fix SPTE encoding of MMIO generation upper half To: "Maciej S. Szmigiero" Cc: Sean Christopherson , Joerg Roedel , Jim Mattson , Wanpeng Li , Vitaly Kuznetsov , Jonathan Corbet , linux-doc@vger.kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org References: <156700708db2a5296c5ed7a8b9ac71f1e9765c85.1607129096.git.maciej.szmigiero@oracle.com> From: Paolo Bonzini Message-ID: <370db207-7216-ae26-0c33-dab61e0fdaab@redhat.com> Date: Sun, 6 Dec 2020 11:09:43 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0 MIME-Version: 1.0 In-Reply-To: <156700708db2a5296c5ed7a8b9ac71f1e9765c85.1607129096.git.maciej.szmigiero@oracle.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 05/12/20 01:48, Maciej S. Szmigiero wrote: > From: "Maciej S. Szmigiero" > > Commit cae7ed3c2cb0 ("KVM: x86: Refactor the MMIO SPTE generation handling") > cleaned up the computation of MMIO generation SPTE masks, however it > introduced a bug how the upper part was encoded: > SPTE bits 52-61 were supposed to contain bits 10-19 of the current > generation number, however a missing shift encoded bits 1-10 there instead > (mostly duplicating the lower part of the encoded generation number that > then consisted of bits 1-9). > > In the meantime, the upper part was shrunk by one bit and moved by > subsequent commits to become an upper half of the encoded generation number > (bits 9-17 of bits 0-17 encoded in a SPTE). > > In addition to the above, commit 56871d444bc4 ("KVM: x86: fix overlap between SPTE_MMIO_MASK and generation") > has changed the SPTE bit range assigned to encode the generation number and > the total number of bits encoded but did not update them in the comment > attached to their defines, nor in the KVM MMU doc. > Let's do it here, too, since it is too trivial thing to warrant a separate > commit. > > Fixes: cae7ed3c2cb0 ("KVM: x86: Refactor the MMIO SPTE generation handling") > Signed-off-by: Maciej S. Szmigiero > --- Good catch. What do you think about this alternative definition? It computes everything from the bit ranges. #define MMIO_SPTE_GEN_LOW_START 3 #define MMIO_SPTE_GEN_LOW_END 11 #define MMIO_SPTE_GEN_HIGH_START PT64_SECOND_AVAIL_BITS_SHIFT #define MMIO_SPTE_GEN_HIGH_END 62 #define MMIO_SPTE_GEN_LOW_MASK GENMASK_ULL(MMIO_SPTE_GEN_LOW_END, \ MMIO_SPTE_GEN_LOW_START) #define MMIO_SPTE_GEN_HIGH_MASK GENMASK_ULL(MMIO_SPTE_GEN_HIGH_END, \ MMIO_SPTE_GEN_HIGH_START) #define MMIO_SPTE_GEN_LOW_BITS (MMIO_SPTE_GEN_LOW_END - MMIO_SPTE_GEN_LOW_START + 1) #define MMIO_SPTE_GEN_HIGH_BITS (MMIO_SPTE_GEN_HIGH_END - MMIO_SPTE_GEN_HIGH_START + 1) #define MMIO_SPTE_GEN_LOW_SHIFT (MMIO_SPTE_GEN_LOW_START - 0) #define MMIO_SPTE_GEN_HIGH_SHIFT (MMIO_SPTE_GEN_HIGH_START - MMIO_SPTE_GEN_LOW_BITS) #define MMIO_SPTE_GEN_MASK GENMASK_ULL(MMIO_SPTE_GEN_LOW_BITS + MMIO_SPTE_GEN_HIGH_BITS - 1, 0) Thanks, Paolo