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 RTLZelxF 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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: On 6/11/2025 7:03 PM, Fuad Tabba wrote: > 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; > LGTM! Reviewed-by: Shivank Garg Thanks, Shivank