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AJvYcCXoR64GFmnPXdD1qG2G70/4aavsaTjV8OycrDkkW5ZDtty0rXACaMVaSYd4kZvva9FDFLr4AtQpLw==@kvack.org X-Gm-Message-State: AOJu0YwoyOdsXk3aks/jJi3bEhkAyXHPE1wePoO/vPxuv9+zv66FUVdB ZHWyo6hI8nvGYPkYsaxV/3G1yhB0AGiTt02MO+Fg4HnLBnHimiPAS7aDSxzF1TRde4oBv3Pclhr V1g== X-Google-Smtp-Source: AGHT+IHEd86idQu16yNMsd/8yL8nqu5HVRSk9EU79tULRTu402KZNrREDQmVRg+XHZj/Hl7vzp0Q2cBjwQ== X-Received: from wma7.prod.google.com ([2002:a05:600c:8907:b0:441:aaa8:fb65]) (user=tabba job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6000:1a87:b0:3a5:1c3c:8d8d with SMTP id ffacd0b85a97d-3a558af983fmr2481697f8f.55.1749648828461; Wed, 11 Jun 2025 06:33:48 -0700 (PDT) Date: Wed, 11 Jun 2025 14:33:20 +0100 In-Reply-To: <20250611133330.1514028-1-tabba@google.com> Mime-Version: 1.0 References: <20250611133330.1514028-1-tabba@google.com> X-Mailer: git-send-email 2.50.0.rc0.642.g800a2b2222-goog Message-ID: <20250611133330.1514028-9-tabba@google.com> Subject: [PATCH v12 08/18] KVM: guest_memfd: Allow host to map guest_memfd pages From: Fuad Tabba To: kvm@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-mm@kvack.org, kvmarm@lists.linux.dev 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, david@redhat.com, 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, tabba@google.com Content-Type: text/plain; charset="UTF-8" X-Stat-Signature: 5g6sb3kdigpixqkcd39uzstpo7dd7god X-Rspamd-Queue-Id: 24AC0120009 X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1749648829-623524 X-HE-Meta: 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 R22Ir9eF 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 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: This patch enables support for shared memory in guest_memfd, including mapping that memory from host userspace. This functionality is gated by the KVM_GMEM_SHARED_MEM Kconfig option, and enabled for a given instance by the GUEST_MEMFD_FLAG_SUPPORT_SHARED flag at creation time. Reviewed-by: Gavin Shan Acked-by: David Hildenbrand Co-developed-by: Ackerley Tng Signed-off-by: Ackerley Tng Signed-off-by: Fuad Tabba --- include/linux/kvm_host.h | 13 +++++++ include/uapi/linux/kvm.h | 1 + virt/kvm/Kconfig | 4 +++ virt/kvm/guest_memfd.c | 73 ++++++++++++++++++++++++++++++++++++++++ 4 files changed, 91 insertions(+) diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 9a6712151a74..6b63556ca150 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -729,6 +729,19 @@ static inline bool kvm_arch_supports_gmem(struct kvm *kvm) } #endif +/* + * Returns true if this VM supports shared mem in guest_memfd. + * + * Arch code must define kvm_arch_supports_gmem_shared_mem if support for + * guest_memfd is enabled. + */ +#if !defined(kvm_arch_supports_gmem_shared_mem) +static inline bool kvm_arch_supports_gmem_shared_mem(struct kvm *kvm) +{ + return false; +} +#endif + #ifndef kvm_arch_has_readonly_mem static inline bool kvm_arch_has_readonly_mem(struct kvm *kvm) { diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h index d00b85cb168c..cb19150fd595 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h @@ -1570,6 +1570,7 @@ 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_SUPPORT_SHARED (1ULL << 0) struct kvm_create_guest_memfd { __u64 size; diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig index 559c93ad90be..e90884f74404 100644 --- a/virt/kvm/Kconfig +++ b/virt/kvm/Kconfig @@ -128,3 +128,7 @@ config HAVE_KVM_ARCH_GMEM_PREPARE config HAVE_KVM_ARCH_GMEM_INVALIDATE bool depends on KVM_GMEM + +config KVM_GMEM_SHARED_MEM + select KVM_GMEM + bool diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c index 6db515833f61..06616b6b493b 100644 --- a/virt/kvm/guest_memfd.c +++ b/virt/kvm/guest_memfd.c @@ -312,7 +312,77 @@ static pgoff_t kvm_gmem_get_index(struct kvm_memory_slot *slot, gfn_t gfn) return gfn - slot->base_gfn + slot->gmem.pgoff; } +static bool kvm_gmem_supports_shared(struct inode *inode) +{ + const u64 flags = (u64)inode->i_private; + + if (!IS_ENABLED(CONFIG_KVM_GMEM_SHARED_MEM)) + return false; + + return flags & GUEST_MEMFD_FLAG_SUPPORT_SHARED; +} + +static vm_fault_t kvm_gmem_fault_shared(struct vm_fault *vmf) +{ + struct inode *inode = file_inode(vmf->vma->vm_file); + struct folio *folio; + vm_fault_t ret = VM_FAULT_LOCKED; + + if (((loff_t)vmf->pgoff << PAGE_SHIFT) >= i_size_read(inode)) + return VM_FAULT_SIGBUS; + + folio = kvm_gmem_get_folio(inode, vmf->pgoff); + if (IS_ERR(folio)) { + int err = PTR_ERR(folio); + + if (err == -EAGAIN) + return VM_FAULT_RETRY; + + return vmf_error(err); + } + + if (WARN_ON_ONCE(folio_test_large(folio))) { + ret = VM_FAULT_SIGBUS; + goto out_folio; + } + + if (!folio_test_uptodate(folio)) { + clear_highpage(folio_page(folio, 0)); + kvm_gmem_mark_prepared(folio); + } + + vmf->page = folio_file_page(folio, vmf->pgoff); + +out_folio: + if (ret != VM_FAULT_LOCKED) { + folio_unlock(folio); + folio_put(folio); + } + + return ret; +} + +static const struct vm_operations_struct kvm_gmem_vm_ops = { + .fault = kvm_gmem_fault_shared, +}; + +static int kvm_gmem_mmap(struct file *file, struct vm_area_struct *vma) +{ + if (!kvm_gmem_supports_shared(file_inode(file))) + return -ENODEV; + + if ((vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) != + (VM_SHARED | VM_MAYSHARE)) { + return -EINVAL; + } + + vma->vm_ops = &kvm_gmem_vm_ops; + + return 0; +} + static struct file_operations kvm_gmem_fops = { + .mmap = kvm_gmem_mmap, .open = generic_file_open, .release = kvm_gmem_release, .fallocate = kvm_gmem_fallocate, @@ -463,6 +533,9 @@ 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_shared_mem(kvm)) + valid_flags |= GUEST_MEMFD_FLAG_SUPPORT_SHARED; + if (flags & ~valid_flags) return -EINVAL; -- 2.50.0.rc0.642.g800a2b2222-goog