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[2003:cb:c72d:2500:94b5:4b7d:ad4a:fd0b]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3978ef9a23bsm14708842f8f.15.2025.03.18.12.35.39 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 18 Mar 2025 12:35:40 -0700 (PDT) Message-ID: Date: Tue, 18 Mar 2025 20:35:38 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/1] KVM: arm64: Allow cacheable stage 2 mapping using VMA flags To: Catalin Marinas , Jason Gunthorpe Cc: Marc Zyngier , Ankit Agrawal , "oliver.upton@linux.dev" , "joey.gouly@arm.com" , "suzuki.poulose@arm.com" , "yuzenghui@huawei.com" , "will@kernel.org" , "ryan.roberts@arm.com" , "shahuang@redhat.com" , "lpieralisi@kernel.org" , Aniket Agashe , Neo Jia , Kirti Wankhede , "Tarun Gupta (SW-GPU)" , Vikram Sethi , Andy Currid , Alistair Popple , John Hubbard , Dan Williams , Zhi Wang , Matt Ochs , Uday Dhoke , Dheeraj Nigam , Krishnakant Jaju , "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" , "ddutile@redhat.com" , "tabba@google.com" , "qperret@google.com" , "seanjc@google.com" , "kvmarm@lists.linux.dev" , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" References: <861pv5p0c3.wl-maz@kernel.org> <86r033olwv.wl-maz@kernel.org> <87tt7y7j6r.wl-maz@kernel.org> <8634fcnh0n.wl-maz@kernel.org> <86wmcmn0dp.wl-maz@kernel.org> <20250318125527.GP9311@nvidia.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: 575CF4000D X-Stat-Signature: i5g9k7jtpjaqa3owp4e38mj3nm4ddt9h X-Rspamd-Server: rspam06 X-HE-Tag: 1742326545-594142 X-HE-Meta: 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 55FEpsAB aHGYuqr6xXW257YLBOQqxZYK7FJ8KblYjBHJZ4oslAeOZ9OS7QLptQAZtXV/0j27B39XSdWxK74xxeAvQtoZuCBnNT5JbuZj2UzxFHlyo+4+34p3wV5Cq06sC1PSFo7tqetVM3UuZiaxq4LhV9jdq5t84MrbcUkxXYKtpaFX92ffqDtlZRE0Z+SiKQGWfKgb04X2zCjI35AGNkBN7WHxmy9Zy/Y7Ea5FluVjaYUcyBl2hT3hWZTAXU48KTsTOGFIK/CH+lfLxOPq+dFSMW7yUmIBnq25K747mHkCyrFywptar6DLwko5B1mAE0XmUBHfRlrbP0op/5dRchxNFx4z/Vz32JKXm/f0MLwB2RK6HW62QOQy5iXGqqruQVduDH9UbBDU8tUaJT+C/rWkNyfi5Mj85UZq0TefU9SZI2sEnqcS6ZPHj1zLhi7c05BRdaE/GRzol 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 18.03.25 20:27, Catalin Marinas wrote: > On Tue, Mar 18, 2025 at 09:55:27AM -0300, Jason Gunthorpe wrote: >> On Tue, Mar 18, 2025 at 09:39:30AM +0000, Marc Zyngier wrote: >>> The memslot must also be created with a new flag ((2c) in the taxonomy >>> above) that carries the "Please map VM_PFNMAP VMAs as cacheable". This >>> flag is only allowed if (1) is valid. >>> >>> This results in the following behaviours: >>> >>> - If the VMM creates the memslot with the cacheable attribute without >>> (1) being advertised, we fail. >>> >>> - If the VMM creates the memslot without the cacheable attribute, we >>> map as NC, as it is today. >> >> Is that OK though? >> >> Now we have the MM page tables mapping this memory as cachable but KVM >> and the guest is accessing it as non-cached. > > I don't think we should allow this. > >> I thought ARM tried hard to avoid creating such mismatches? This is >> why the pgprot flags were used to drive this, not an opt-in flag. To >> prevent userspace from forcing a mismatch. > > We have the vma->vm_page_prot when the memslot is added, so we could use > this instead of additional KVM flags. I thought we try to avoid messing with the VMA when adding memslots; because KVM_CAP_SYNC_MMU allows user space for changing the VMAs afterwards without changing the memslot? include/uapi/linux/kvm.h:#define KVM_CAP_SYNC_MMU 16 /* Changes to host mmap are reflected in guest */ -- Cheers, David / dhildenb