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[2003:cb:c70b:b400:e20a:6d03:7ac8:f97d]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-438b16ff48esm42826635e9.0.2025.01.23.02.28.00 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 23 Jan 2025 02:28:01 -0800 (PST) Message-ID: Date: Thu, 23 Jan 2025 11:27:59 +0100 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v1 1/9] KVM: guest_memfd: Allow host to mmap guest_memfd() pages To: Fuad Tabba Cc: kvm@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-mm@kvack.org, 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, xiaoyao.li@intel.com, yilun.xu@intel.com, chao.p.peng@linux.intel.com, jarkko@kernel.org, amoorthy@google.com, dmatlack@google.com, yu.c.zhang@linux.intel.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 References: <20250122152738.1173160-1-tabba@google.com> <20250122152738.1173160-2-tabba@google.com> <647bbdac-df82-4cdb-a3e9-287d439b4ef7@redhat.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit >>> + bool >>> diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c >>> index 47a9f68f7b24..9ee162bf6bde 100644 >>> --- a/virt/kvm/guest_memfd.c >>> +++ b/virt/kvm/guest_memfd.c >>> @@ -307,7 +307,78 @@ static pgoff_t kvm_gmem_get_index(struct kvm_memory_slot *slot, gfn_t gfn) >>> return gfn - slot->base_gfn + slot->gmem.pgoff; >>> } >>> >>> +#ifdef CONFIG_KVM_GMEM_MAPPABLE >>> +static vm_fault_t kvm_gmem_fault(struct vm_fault *vmf) >>> +{ >>> + struct inode *inode = file_inode(vmf->vma->vm_file); >>> + struct folio *folio; >>> + vm_fault_t ret = VM_FAULT_LOCKED; >>> + >>> + filemap_invalidate_lock_shared(inode->i_mapping); >>> + >>> + folio = kvm_gmem_get_folio(inode, vmf->pgoff); >> >> >> Would the idea be later that kvm_gmem_get_folio() would fail on private >> memory, or do you envision other checks in this code here in the future? > > There would be other checks in the future, the idea is that they would > be the ones in: > https://lore.kernel.org/all/20250117163001.2326672-8-tabba@google.com/ > Thanks, so I wonder if this patch should just add necessary callback(s) as well, to make this patch look like it adds most of the infrastructure on the mmap level. kvm_gmem_is_shared() or sth like that, documenting that it must be called after kvm_gmem_get_folio() -- with a raised folio reference / folio lock. Alternatively, provide a kvm_gmem_get_shared_folio() that abstracts that operation. We could also for now ensure that we really only get small folios back, and even get rid of the clearing loop. The "WARN_ON_ONCE(folio_test_guestmem(folio)" would be added separately. In the context of this series, the callback would be a nop and always say "yes". -- Cheers, David / dhildenb