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[2003:d8:2f1d:ed00:1769:dd7c:7208:eb33]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3b5e8e14d07sm17694498f8f.66.2025.07.16.03.31.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 16 Jul 2025 03:31:50 -0700 (PDT) Message-ID: Date: Wed, 16 Jul 2025 12:31:47 +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 v14 09/21] KVM: guest_memfd: Track guest_memfd mmap support in memslot To: Fuad Tabba , Xiaoyao Li Cc: kvm@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-mm@kvack.org, kvmarm@lists.linux.dev, pbonzini@redhat.com, chenhuacai@kernel.org, mpe@ellerman.id.au, anup@brainfault.org, paul.walmsley@sifive.com, palmer@dabbelt.com, aou@eecs.berkeley.edu, seanjc@google.com, viro@zeniv.linux.org.uk, brauner@kernel.org, willy@infradead.org, akpm@linux-foundation.org, yilun.xu@intel.com, chao.p.peng@linux.intel.com, jarkko@kernel.org, amoorthy@google.com, dmatlack@google.com, isaku.yamahata@intel.com, mic@digikod.net, vbabka@suse.cz, vannapurve@google.com, ackerleytng@google.com, mail@maciej.szmigiero.name, michael.roth@amd.com, wei.w.wang@intel.com, liam.merwick@oracle.com, isaku.yamahata@gmail.com, kirill.shutemov@linux.intel.com, suzuki.poulose@arm.com, steven.price@arm.com, quic_eberman@quicinc.com, quic_mnalajal@quicinc.com, quic_tsoni@quicinc.com, quic_svaddagi@quicinc.com, quic_cvanscha@quicinc.com, quic_pderrin@quicinc.com, quic_pheragu@quicinc.com, catalin.marinas@arm.com, james.morse@arm.com, yuzenghui@huawei.com, oliver.upton@linux.dev, maz@kernel.org, will@kernel.org, qperret@google.com, keirf@google.com, roypat@amazon.co.uk, shuah@kernel.org, hch@infradead.org, jgg@nvidia.com, rientjes@google.com, jhubbard@nvidia.com, fvdl@google.com, hughd@google.com, jthoughton@google.com, peterx@redhat.com, pankaj.gupta@amd.com, ira.weiny@intel.com References: <20250715093350.2584932-1-tabba@google.com> <20250715093350.2584932-10-tabba@google.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 16.07.25 10:21, Fuad Tabba wrote: > Hi Xiaoyao, > > On Wed, 16 Jul 2025 at 07:11, Xiaoyao Li wrote: >> >> On 7/15/2025 5:33 PM, Fuad Tabba wrote: >>> Add a new internal flag, KVM_MEMSLOT_GMEM_ONLY, to the top half of >>> memslot->flags. This flag tracks when a guest_memfd-backed memory slot >>> supports host userspace mmap operations. It's strictly for KVM's >>> internal use. >> >> I would expect some clarification of why naming it with >> KVM_MEMSLOT_GMEM_ONLY, not something like KVM_MEMSLOT_GMEM_MMAP_ENABLED >> >> There was a patch to check the userspace_addr of the memslot refers to >> the same memory as guest memfd[1], but that patch was dropped. Without >> the background that when guest memfd is mmapable, userspace doesn't need >> to provide separate memory via userspace_addr, it's hard to understand >> and accept the name of GMEM_ONLY. > > The commit message could have clarified this a bit more. Regarding the > rationale for the naming, there have been various threads and live > discussions in the biweekly guest_memfd meeting . Instead of rehashing > the discussion here, I can refer you to a couple [1, 2]. Maybe clarify here: "Add a new internal flag, KVM_MEMSLOT_GMEM_ONLY, to the top half of memslot->flags. This flag tracks when a guest_memfd-backed memory slot supports host userspace mmap operations, which implies that all memory, not just private memory for CoCo VMs, is consumed through guest_memfd: "gmem only" And add a pointer to the list discussion. -- Cheers, David / dhildenb