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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 Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: 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 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