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[2003:d8:2f25:9c00:e2c7:6eb5:8a51:1c60]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a35ca88735sm19296243f8f.69.2025.05.21.00.48.42 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 21 May 2025 00:48:44 -0700 (PDT) Message-ID: Date: Wed, 21 May 2025 09:48:41 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v9 09/17] KVM: x86/mmu: Handle guest page faults for guest_memfd with shared memory To: Fuad Tabba , kvm@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-mm@kvack.org Cc: 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, 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: <20250513163438.3942405-1-tabba@google.com> <20250513163438.3942405-10-tabba@google.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: EAC7710000C X-Rspam-User: X-Stat-Signature: mkdpe4qiz4sh7q7o9ce1xjpry7or4h3d X-HE-Tag: 1747813729-303289 X-HE-Meta: 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 Ejan9FhF FFP5LnL1VRLbTOJJ0/q02SFbK3TU5H5uJNIiDdQ6hXakVLaCaVUW6Qd1xJs+7JdZsNuJ0c3C2tLg0E9MyaMw4NNiQCTFI3hZ1cgQ9v2VGhTzAwA6K8bq0BmjxjvEpwP2eHT2Xp4CQ/dlkJ37dWUf3E9csvXIUMl1MEYj1o+Mw8ZmG6rTlQMLb159yN1Ql3+mssSAc X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 13.05.25 18:34, Fuad Tabba wrote: > From: Ackerley Tng > > For memslots backed by guest_memfd with shared mem support, the KVM MMU > always faults-in pages from guest_memfd, and not from the userspace_addr. > Towards this end, this patch also introduces a new guest_memfd flag, > GUEST_MEMFD_FLAG_SUPPORT_SHARED, which indicates that the guest_memfd > instance supports in-place shared memory. > > This flag is only supported if the VM creating the guest_memfd instance > belongs to certain types determined by architecture. Only non-CoCo VMs > are permitted to use guest_memfd with shared mem, for now. > > Function names have also been updated for accuracy - > kvm_mem_is_private() returns true only when the current private/shared > state (in the CoCo sense) of the memory is private, and returns false if > the current state is shared explicitly or impicitly, e.g., belongs to a > non-CoCo VM. > > kvm_mmu_faultin_pfn_gmem() is updated to indicate that it can be used > to fault in not just private memory, but more generally, from > guest_memfd. > > Co-developed-by: Fuad Tabba > Signed-off-by: Fuad Tabba > Co-developed-by: David Hildenbrand > Signed-off-by: David Hildenbrand > Signed-off-by: Ackerley Tng > --- [...] > + > #ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES > static inline unsigned long kvm_get_memory_attributes(struct kvm *kvm, gfn_t gfn) > { > @@ -2515,10 +2524,30 @@ bool kvm_arch_pre_set_memory_attributes(struct kvm *kvm, > bool kvm_arch_post_set_memory_attributes(struct kvm *kvm, > struct kvm_gfn_range *range); > > +/* > + * Returns true if the given gfn's private/shared status (in the CoCo sense) is > + * private. > + * > + * A return value of false indicates that the gfn is explicitly or implicity s/implicity/implicitly/ > + * shared (i.e., non-CoCo VMs). > + */ > static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn) > { > - return IS_ENABLED(CONFIG_KVM_GMEM) && > - kvm_get_memory_attributes(kvm, gfn) & KVM_MEMORY_ATTRIBUTE_PRIVATE; > + struct kvm_memory_slot *slot; > + > + if (!IS_ENABLED(CONFIG_KVM_GMEM)) > + return false; > + > + slot = gfn_to_memslot(kvm, gfn); > + if (kvm_slot_has_gmem(slot) && kvm_gmem_memslot_supports_shared(slot)) { > + /* > + * For now, memslots only support in-place shared memory if the > + * host is allowed to mmap memory (i.e., non-Coco VMs). > + */ Not accurate: there is no in-place conversion support in this series, because there is no such itnerface. So the reason is that all memory is shared for there VM types? > + return false; > + } > + > + return kvm_get_memory_attributes(kvm, gfn) & KVM_MEMORY_ATTRIBUTE_PRIVATE; > } > #else > static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn) > diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c > index 2f499021df66..fe0245335c96 100644 > --- a/virt/kvm/guest_memfd.c > +++ b/virt/kvm/guest_memfd.c > @@ -388,6 +388,23 @@ static int kvm_gmem_mmap(struct file *file, struct vm_area_struct *vma) > > return 0; > } > + > +bool kvm_gmem_memslot_supports_shared(const struct kvm_memory_slot *slot) > +{ > + struct file *file; > + bool ret; > + > + file = kvm_gmem_get_file((struct kvm_memory_slot *)slot); > + if (!file) > + return false; > + > + ret = kvm_gmem_supports_shared(file_inode(file)); > + > + fput(file); > + return ret; Would it make sense to cache that information in the memslot, to avoid the get/put? We could simply cache when creating the memslot I guess. As an alternative ... could we simple get/put when managing the memslot? -- Cheers, David / dhildenb