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[142.162.112.119]) by smtp.gmail.com with ESMTPSA id af79cd13be357-8c711d29aa2sm294243485a.35.2026.01.28.16.37.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 28 Jan 2026 16:37:53 -0800 (PST) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1vlG2j-00000009g5p-04Lm; Wed, 28 Jan 2026 20:37:53 -0400 Date: Wed, 28 Jan 2026 20:37:53 -0400 From: Jason Gunthorpe To: Ackerley Tng Cc: Alexey Kardashevskiy , cgroups@vger.kernel.org, kvm@vger.kernel.org, linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, x86@kernel.org, akpm@linux-foundation.org, binbin.wu@linux.intel.com, bp@alien8.de, brauner@kernel.org, chao.p.peng@intel.com, chenhuacai@kernel.org, corbet@lwn.net, dave.hansen@intel.com, dave.hansen@linux.intel.com, david@redhat.com, dmatlack@google.com, erdemaktas@google.com, fan.du@intel.com, fvdl@google.com, haibo1.xu@intel.com, hannes@cmpxchg.org, hch@infradead.org, hpa@zytor.com, hughd@google.com, ira.weiny@intel.com, isaku.yamahata@intel.com, jack@suse.cz, james.morse@arm.com, jarkko@kernel.org, jgowans@amazon.com, jhubbard@nvidia.com, jroedel@suse.de, jthoughton@google.com, jun.miao@intel.com, kai.huang@intel.com, keirf@google.com, kent.overstreet@linux.dev, liam.merwick@oracle.com, maciej.wieczor-retman@intel.com, mail@maciej.szmigiero.name, maobibo@loongson.cn, mathieu.desnoyers@efficios.com, maz@kernel.org, mhiramat@kernel.org, mhocko@kernel.org, mic@digikod.net, michael.roth@amd.com, mingo@redhat.com, mlevitsk@redhat.com, mpe@ellerman.id.au, muchun.song@linux.dev, nikunj@amd.com, nsaenz@amazon.es, oliver.upton@linux.dev, palmer@dabbelt.com, pankaj.gupta@amd.com, paul.walmsley@sifive.com, pbonzini@redhat.com, peterx@redhat.com, pgonda@google.com, prsampat@amd.com, pvorel@suse.cz, qperret@google.com, richard.weiyang@gmail.com, rick.p.edgecombe@intel.com, rientjes@google.com, rostedt@goodmis.org, roypat@amazon.co.uk, rppt@kernel.org, seanjc@google.com, shakeel.butt@linux.dev, shuah@kernel.org, steven.price@arm.com, steven.sistare@oracle.com, suzuki.poulose@arm.com, tabba@google.com, tglx@linutronix.de, thomas.lendacky@amd.com, vannapurve@google.com, vbabka@suse.cz, viro@zeniv.linux.org.uk, vkuznets@redhat.com, wei.w.wang@intel.com, will@kernel.org, willy@infradead.org, wyihan@google.com, xiaoyao.li@intel.com, yan.y.zhao@intel.com, yilun.xu@intel.com, yuzenghui@huawei.com, zhiquan1.li@intel.com Subject: Re: [RFC PATCH v1 05/37] KVM: guest_memfd: Wire up kvm_get_memory_attributes() to per-gmem attributes Message-ID: <20260129003753.GZ1641016@ziepe.ca> References: <071a3c6603809186e914fe5fed939edee4e11988.1760731772.git.ackerleytng@google.com> <07836b1d-d0d8-40f2-8f7b-7805beca31d0@amd.com> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Wed, Jan 28, 2026 at 01:47:50PM -0800, Ackerley Tng wrote: > Alexey Kardashevskiy writes: > > > > > [...snip...] > > > > > > Thanks for bringing this up! > > > I am trying to make it work with TEE-IO where fd of VFIO MMIO is a dmabuf fd while the rest (guest RAM) is gmemfd. The above suggests that if there is gmemfd - then the memory attributes are handled by gmemfd which is... expected? > > > > I think this is not expected. > > IIUC MMIO guest physical addresses don't have an associated memslot, but > if you managed to get to that line in kvm_gmem_get_memory_attributes(), > then there is an associated memslot (slot != NULL)? I think they should have a memslot, shouldn't they? I imagine creating a memslot from a FD and the FD can be memfd, guestmemfd, dmabuf, etc, etc ? > Either way, guest_memfd shouldn't store attributes for guest physical > addresses that don't belong to some guest_memfd memslot. > > I think we need a broader discussion for this on where to store memory > attributes for MMIO addresses. > > I think we should at least have line of sight to storing memory > attributes for MMIO addresses, in case we want to design something else, > since we're putting vm_memory_attributes on a deprecation path with this > series. I don't know where you want to store them in KVM long term, but they need to come from the dmabuf itself (probably via a struct p2pdma_provider) and currently it is OK to assume all DMABUFs are uncachable MMIO that is safe for the VM to convert into "write combining" (eg Normal-NC on ARM) Jason