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[2003:d8:2f2c:5500:988:23f9:faa0:7232]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-454a9bde3b9sm55238795e9.28.2025.07.04.05.21.32 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 04 Jul 2025 05:21:34 -0700 (PDT) Message-ID: <4b06b163-e1ce-4c20-b878-4593bc86bf53@redhat.com> Date: Fri, 4 Jul 2025 14:21:32 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v9 3/6] KVM: arm64: Block cacheable PFNMAP mapping To: Jason Gunthorpe , Ankit Agrawal Cc: Will Deacon , "maz@kernel.org" , "oliver.upton@linux.dev" , "joey.gouly@arm.com" , "suzuki.poulose@arm.com" , "yuzenghui@huawei.com" , "catalin.marinas@arm.com" , "ryan.roberts@arm.com" , "shahuang@redhat.com" , "lpieralisi@kernel.org" , "ddutile@redhat.com" , "seanjc@google.com" , Aniket Agashe , Neo Jia , Kirti Wankhede , Krishnakant Jaju , "Tarun Gupta (SW-GPU)" , Vikram Sethi , Andy Currid , Alistair Popple , John Hubbard , Dan Williams , Zhi Wang , Matt Ochs , Uday Dhoke , Dheeraj Nigam , "alex.williamson@redhat.com" , "sebastianene@google.com" , "coltonlewis@google.com" , "kevin.tian@intel.com" , "yi.l.liu@intel.com" , "ardb@kernel.org" , "akpm@linux-foundation.org" , "gshan@redhat.com" , "linux-mm@kvack.org" , "tabba@google.com" , "qperret@google.com" , "kvmarm@lists.linux.dev" , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "maobibo@loongson.cn" , "pbonzini@redhat.com" References: <20250621042111.3992-1-ankita@nvidia.com> <20250621042111.3992-4-ankita@nvidia.com> <20250630122501.GQ167785@nvidia.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 8AF5F16000B X-Stat-Signature: z7ij93nnoejtkqi345zjxo9qukxg14r3 X-Rspam-User: X-HE-Tag: 1751631698-36746 X-HE-Meta: U2FsdGVkX18XQxsVb+SCg1m8XrufGiCixk9KBF6sxKIN/cHbLXicuwfCiZXMYnYj2alSBX/uG5NtYuYoc1OPKIW1MaihnYafONkwDVTgv5dPGtwGEoSLSDLQjLx7T6HVszzv6zKJzLhzSBSK6C5+DsoYusmXBuxqCw1L9dmKmzXuRQaHnEZCtBcQh8uVt92GvVXmmmLHCVcow1GPgqhGgkq4Qx5vp3RctyE9cTLh2PPnPqrvAsawsAJbloq2/XXbLkTlBL6CveMVCvr5rQ02H3WD+Zs1xUXUcdsVItjIw/AhU4oeObzZVm+LJYK3MvtakpY0LCZA3zD8lWFhPjeOC8LNqjUdyFc0d+6uROjR0MVZEWIOstMx8YxyiUGXEaKBY5lM+i5WUYznvgIQNfWrEX4i8iSqi8X7KEFsaGExCuQeWOL+X6kxfvPPQaeBXLuTJ+FW1G1CBhjKyI6qiuTY5Sar4txaa/DkH6Q4HHJqnC2phtOKCyLl+fPOGFOlbrP2Ovmpc8dxWH8KdkDbfCTuY+6SqPeu3lYmVEtq6uz2TnPeQ5tc6QnU7ORBlnhhiyuQZEhqoIsif/X4ZeYU8hPrySsijDnZz29x3QckbfhrmuZ4RUqVUqYirc0Zg2ktX9uFmt4B5R+hRgmAVKTYBOqyVEa1SGm2AYtiUMgjRHuANNrTw77dLB/ZyHoXuNeIvLM/qKuJkuEimSmiXZkzpZJ8BhlhMRv3i/NVIdDgD2R2eSCqy4vQ14F5na9KItOg1/wbJZBuQa0UbwmDpU3+ZzPQGk4sdm1Dmq88nVJ2UJR0xELwHfubBjkThrgpg5qpTmWdxZPYYEdqEPfoHucdSjfi11nR+B2lAOTJRZKtTtRURkYAaaK3FkowcAI9o2R/hhdoyDuxBaxBtzIDF/OSHcvDuOhhN5jU97SPu3ENwno6KKEcQJFdM8FBbCLd/e7yaw+Ca+mLeJDlk2gOWgxBkYM 4Sfmhb5R 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 30.06.25 14:25, Jason Gunthorpe wrote: > On Mon, Jun 30, 2025 at 01:56:43AM +0000, Ankit Agrawal wrote: >>> Sorry for the drive-by comment, but I was looking at this old series from >>> Paolo (look at the cover letter and patch 5): >>> >>> https://lore.kernel.org/r/20250109133817.314401-1-pbonzini@redhat.com >>> >>> in which he points out that the arm64 get_vma_page_shift() function >>> incorrectly assumes that a VM_PFNMAP VMA is physically contiguous, which >>> may not be the case if a driver calls remap_pfn_range() to mess around >>> with mappings within the VMA. I think that implies that the optimisation >>> in 2aa53d68cee6 ("KVM: arm64: Try stage2 block mapping for host device >>> MMIO") is unsound. >> >> Hm yeah, that does seem problematic. Perhaps we need a new >> vma flag that could help the driver communicate to the KVM that the >> mapping is contiguous and it can go ahead with the optimization? >> E.g. something similar to VM_ALLOW_ANY_UNCACHED. > > I think Paolo has the right direction - remove any attempts by KVM to > expand contiguity, it should only copy the primary's PTEs and rely on > the primary to discover contiguity. No new flags. 100% -- Cheers, David / dhildenb