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AJvYcCV+9cvWFImw+DXMm4TbSFezHzKXu7p8BJoR2cBIlgFvn3nZqu2kHWGXu5pK2ZZH/8Y0OLFhqgoXCm9/SanM@vger.kernel.org X-Gm-Message-State: AOJu0YwCE5I16J/0R0R4uSDzyBJCq6QZhFwUb5yBVrIrztXecmzosJxv ZehsYtaj5PhQ3n8TzOrOBiyYtji4mfQh0yR6k21NqfDpTKi7AfzfCETJG96g6AsYepp+NEfxbgz /TA== X-Google-Smtp-Source: AGHT+IFsSXSPsIzzjG8cSs5qmMKIcMNndtU6bT4BIo+LmuAUzRynITV3oecnA+zrz7m1ALSccrGRPAfFeQ== X-Received: from wmbel20.prod.google.com ([2002:a05:600c:3e14:b0:450:d104:29f8]) (user=tabba job=prod-delivery.src-stubby-dispatcher) by 2002:a05:600c:1986:b0:442:ff8e:11ac with SMTP id 5b1f17b1804b1-451f0a74b01mr79236105e9.12.1749137899065; Thu, 05 Jun 2025 08:38:19 -0700 (PDT) Date: Thu, 5 Jun 2025 16:37:50 +0100 In-Reply-To: <20250605153800.557144-1-tabba@google.com> Precedence: bulk X-Mailing-List: linux-arm-msm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250605153800.557144-1-tabba@google.com> X-Mailer: git-send-email 2.49.0.1266.g31b7d2e469-goog Message-ID: <20250605153800.557144-9-tabba@google.com> Subject: [PATCH v11 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 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. 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 | 76 ++++++++++++++++++++++++++++++++++++++++ 4 files changed, 94 insertions(+) diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 80371475818f..640ce714cfb2 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 b6ae8ad8934b..c2714c9d1a0e 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h @@ -1566,6 +1566,7 @@ 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..7a158789d1df 100644 --- a/virt/kvm/guest_memfd.c +++ b/virt/kvm/guest_memfd.c @@ -312,7 +312,79 @@ 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) +{ + u64 flags; + + if (!IS_ENABLED(CONFIG_KVM_GMEM_SHARED_MEM)) + return false; + + flags = (u64)inode->i_private; + + 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, @@ -428,6 +500,7 @@ static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags) } file->f_flags |= O_LARGEFILE; + allow_write_access(file); inode = file->f_inode; WARN_ON(file->f_mapping != inode->i_mapping); @@ -463,6 +536,9 @@ 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;