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Tue, 29 Jul 2025 15:56:07 -0700 (PDT) Date: Tue, 29 Jul 2025 15:54:52 -0700 In-Reply-To: <20250729225455.670324-1-seanjc@google.com> Mime-Version: 1.0 References: <20250729225455.670324-1-seanjc@google.com> X-Mailer: git-send-email 2.50.1.552.g942d659e1b-goog Message-ID: <20250729225455.670324-22-seanjc@google.com> Subject: [PATCH v17 21/24] KVM: Allow and advertise support for host mmap() on guest_memfd files From: Sean Christopherson To: Paolo Bonzini , Marc Zyngier , Oliver Upton , Sean Christopherson Cc: kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org, Ira Weiny , Gavin Shan , Shivank Garg , Vlastimil Babka , Xiaoyao Li , David Hildenbrand , Fuad Tabba , Ackerley Tng , Tao Chan , James Houghton Content-Type: text/plain; charset="UTF-8" X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250729_155608_538517_185343B9 X-CRM114-Status: GOOD ( 14.95 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Sean Christopherson Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org From: Fuad Tabba Now that all the x86 and arm64 plumbing for mmap() on guest_memfd is in place, allow userspace to set GUEST_MEMFD_FLAG_MMAP and advertise support via a new capability, KVM_CAP_GUEST_MEMFD_MMAP. The availability of this capability is determined per architecture, and its enablement for a specific guest_memfd instance is controlled by the GUEST_MEMFD_FLAG_MMAP flag at creation time. Update the KVM API documentation to detail the KVM_CAP_GUEST_MEMFD_MMAP capability, the associated GUEST_MEMFD_FLAG_MMAP, and provide essential information regarding support for mmap in guest_memfd. Reviewed-by: David Hildenbrand Reviewed-by: Gavin Shan Reviewed-by: Shivank Garg Reviewed-by: Xiaoyao Li Signed-off-by: Fuad Tabba Signed-off-by: Sean Christopherson --- Documentation/virt/kvm/api.rst | 9 +++++++++ include/uapi/linux/kvm.h | 2 ++ virt/kvm/guest_memfd.c | 7 ++++++- virt/kvm/kvm_main.c | 2 ++ 4 files changed, 19 insertions(+), 1 deletion(-) diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index fcb783735dd1..1e0c4a68876d 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -6414,6 +6414,15 @@ most one mapping per page, i.e. binding multiple memory regions to a single guest_memfd range is not allowed (any number of memory regions can be bound to a single guest_memfd file, but the bound ranges must not overlap). +When the capability KVM_CAP_GUEST_MEMFD_MMAP is supported, the 'flags' field +supports GUEST_MEMFD_FLAG_MMAP. Setting this flag on guest_memfd creation +enables mmap() and faulting of guest_memfd memory to host userspace. + +When the KVM MMU performs a PFN lookup to service a guest fault and the backing +guest_memfd has the GUEST_MEMFD_FLAG_MMAP set, then the fault will always be +consumed from guest_memfd, regardless of whether it is a shared or a private +fault. + See KVM_SET_USER_MEMORY_REGION2 for additional details. 4.143 KVM_PRE_FAULT_MEMORY diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h index aeb2ca10b190..0d96d2ae6e5d 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h @@ -961,6 +961,7 @@ struct kvm_enable_cap { #define KVM_CAP_ARM_EL2 240 #define KVM_CAP_ARM_EL2_E2H0 241 #define KVM_CAP_RISCV_MP_STATE_RESET 242 +#define KVM_CAP_GUEST_MEMFD_MMAP 243 struct kvm_irq_routing_irqchip { __u32 irqchip; @@ -1597,6 +1598,7 @@ struct kvm_memory_attributes { #define KVM_MEMORY_ATTRIBUTE_PRIVATE (1ULL << 3) #define KVM_CREATE_GUEST_MEMFD _IOWR(KVMIO, 0xd4, struct kvm_create_guest_memfd) +#define GUEST_MEMFD_FLAG_MMAP (1ULL << 0) struct kvm_create_guest_memfd { __u64 size; diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c index d5b445548af4..08a6bc7d25b6 100644 --- a/virt/kvm/guest_memfd.c +++ b/virt/kvm/guest_memfd.c @@ -314,7 +314,9 @@ static pgoff_t kvm_gmem_get_index(struct kvm_memory_slot *slot, gfn_t gfn) static bool kvm_gmem_supports_mmap(struct inode *inode) { - return false; + const u64 flags = (u64)inode->i_private; + + return flags & GUEST_MEMFD_FLAG_MMAP; } static vm_fault_t kvm_gmem_fault_user_mapping(struct vm_fault *vmf) @@ -522,6 +524,9 @@ int kvm_gmem_create(struct kvm *kvm, struct kvm_create_guest_memfd *args) u64 flags = args->flags; u64 valid_flags = 0; + if (kvm_arch_supports_gmem_mmap(kvm)) + valid_flags |= GUEST_MEMFD_FLAG_MMAP; + if (flags & ~valid_flags) return -EINVAL; diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 4f57cb92e109..18f29ef93543 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -4918,6 +4918,8 @@ static int kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg) #ifdef CONFIG_KVM_GUEST_MEMFD case KVM_CAP_GUEST_MEMFD: return 1; + case KVM_CAP_GUEST_MEMFD_MMAP: + return !kvm || kvm_arch_supports_gmem_mmap(kvm); #endif default: break; -- 2.50.1.552.g942d659e1b-goog