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Received: from CH3PR12MB8659.namprd12.prod.outlook.com (2603:10b6:610:17c::13) by CY8PR12MB7684.namprd12.prod.outlook.com (2603:10b6:930:87::16) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.8356.15; Fri, 17 Jan 2025 19:16:06 +0000 Received: from CH3PR12MB8659.namprd12.prod.outlook.com ([fe80::6eb6:7d37:7b4b:1732]) by CH3PR12MB8659.namprd12.prod.outlook.com ([fe80::6eb6:7d37:7b4b:1732%5]) with mapi id 15.20.8356.010; Fri, 17 Jan 2025 19:16:06 +0000 Date: Fri, 17 Jan 2025 15:16:04 -0400 From: Jason Gunthorpe To: Catalin Marinas Cc: Ankit Agrawal , David Hildenbrand , "maz@kernel.org" , "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 , "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" , "kvmarm@lists.linux.dev" , "kvm@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCH v2 1/1] KVM: arm64: Allow cacheable stage 2 mapping using VMA flags Message-ID: <20250117191604.GF5556@nvidia.com> References: <20250113162749.GN5556@nvidia.com> <0743193c-80a0-4ef8-9cd7-cb732f3761ab@redhat.com> <20250114133145.GA5556@nvidia.com> <20250115143213.GQ5556@nvidia.com> <20250117140050.GC5556@nvidia.com> Content-Type: text/plain; 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Or, a bigger > > > happen, disable MTE in guests (well, not that big, not many platforms > > > supporting MTE, especially in the enterprise space). > > > > As above, it seems we already effectively disable MTE in guests to use > > VFIO. > > That's fine. Once the NoTagAccess feature gets in, we could allow MTE > here as well. Yes, we can eventually mark these pages as NoTagAccess and maybe someday consume a VMA flag from VFIO indicating that MTE works and NoTagAccess is not required. > I agree this is safe. My point was more generic about not allowing > cacheable mappings without some sanity check. Ankit's patch relies on > the pgprot used on the S1 mapping to make this decision. Presumably the > pgprot is set by the host driver. Yes, pgprot is set only by vfio, and pgprot == Normal is the sanity check for KVM. > > For this series it is only about mapping VMAs. Some future FD based > > mapping for CC is going to also need similar metadata.. I have another > > thread about that :) > > How soon would you need that and if you come up with a different > mechanism, shouldn't we unify them early rather than having two methods? Looks to me like a year and half or more to negotiate this and complete the required preperation patches. It is big and complex and consensus is not obviously converging.. If we had a FD flow now I'd prefer to use it than going through the VMA :( I have a vauge hope that perhaps KVM could see the VMA when it creates the memslot and then transparently pick up the FD under the VMA and switch to a singular FD based mode inside KVM. Jason