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([2a09:80c0:192:0:5dac:bf3d:c41:c3e7]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a6e805e828sm1794502f8f.32.2025.06.24.04.44.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 24 Jun 2025 04:44:03 -0700 (PDT) Message-ID: <11b23ea3-cadd-442b-88d7-491bba99dabe@redhat.com> Date: Tue, 24 Jun 2025 13:44:00 +0200 Precedence: bulk X-Mailing-List: linux-arm-msm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v12 00/18] KVM: Mapping guest_memfd backed memory at the host for software protected VMs To: Fuad Tabba Cc: Sean Christopherson , 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, 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, 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: <20250611133330.1514028-1-tabba@google.com> <80e062dd-2445-45a6-ba4a-8f5fe3286909@redhat.com> <372bbfa5-1869-4bf2-9c16-0b828cdb86f5@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 On 24.06.25 12:25, Fuad Tabba wrote: > Hi David, > > On Tue, 24 Jun 2025 at 11:16, David Hildenbrand wrote: >> >> On 24.06.25 12:02, Fuad Tabba wrote: >>> Hi, >>> >>> Before I respin this, I thought I'd outline the planned changes for >>> V13, especially since it involves a lot of repainting. I hope that >>> by presenting this first, we could reduce the number of times I'll >>> need to respin it. >>> >>> In struct kvm_arch: add bool supports_gmem instead of renaming >>> has_private_mem >>> >>> The guest_memfd flag GUEST_MEMFD_FLAG_SUPPORT_SHARED should be >>> called GUEST_MEMFD_FLAG_MMAP >>> >>> The memslot internal flag KVM_MEMSLOT_SUPPORTS_GMEM_SHARED should be >>> called KVM_MEMSLOT_SUPPORTS_GMEM_MMAP >>> >>> kvm_arch_supports_gmem_shared_mem() should be called >>> kvm_arch_supports_gmem_mmap() >>> >>> kvm_gmem_memslot_supports_shared() should be called >>> kvm_gmem_memslot_supports_mmap() >>> >>> kvm_gmem_fault_shared(struct vm_fault *vmf) should be called >>> kvm_gmem_fault_user_mapping(struct vm_fault *vmf) >>> >>> The capability KVM_CAP_GMEM_SHARED_MEM should be called >>> KVM_CAP_GMEM_MMAP >>> >>> The Kconfig CONFIG_KVM_GMEM_SHARED_MEM should be called >>> CONFIG_KVM_GMEM_SUPPORTS_MMAP >> >> Works for me. >> >>> >>> Also, what (unless you disagree) will stay the same as V12: >>> >>> Rename CONFIG_KVM_PRIVATE_MEM to CONFIG_KVM_GMEM: Since private >>> implies gmem, and we will have additional flags for MMAP support >> >> Agreed. >> >>> >>> Rename CONFIG_KVM_GENERIC_PRIVATE_MEM to >>> CONFIG_KVM_GENERIC_GMEM_POPULATE >> >> Agreed. >> >>> >>> Rename kvm_slot_can_be_private() to kvm_slot_has_gmem(): since >>> private does imply that it has gmem >> >> Right. It's a little more tricky in reality at least with this series: >> without in-place conversion, not all gmem can have private memory. But >> the places that check kvm_slot_can_be_private() likely only care about >> if this memslot is backed by gmem. > > Exactly. Reading the code, all the places that check > kvm_slot_can_be_private() are really checking whether the slot has > gmem. After this series, if a caller is interested in finding out > whether a slot can be private could achieve the same effect by > checking that a gmem slot doesn't support mmap (i.e., > kvm_slot_has_gmem() && kvm_arch_supports_gmem_mmap() ). If that > happens, we can reintroduce kvm_slot_can_be_private() as such. > > Otherwise, I could keep it and already define it as so. What do you think? > >> Sean also raised a "kvm_is_memslot_gmem_only()", how did you end up >> calling that? > > Good point, I'd missed that. Isn't it true that > kvm_is_memslot_gmem_only() is synonymous (at least for now) with > kvm_gmem_memslot_supports_mmap()? Yes. I think having a simple kvm_is_memslot_gmem_only() helper might make fault handling code easier to read, though. -- Cheers, David / dhildenb