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[2003:d8:2f28:de00:1efe:3ea4:63ba:1713]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3b61ca2bf82sm13809742f8f.26.2025.07.22.08.18.46 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 22 Jul 2025 08:18:48 -0700 (PDT) Message-ID: <1e37e4e7-aa7b-4a2a-b1aa-1243f8094dcb@redhat.com> Date: Tue, 22 Jul 2025 17:18:45 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V9 1/7] KVM: guest_memfd: Use guest mem inodes instead of anonymous inodes To: Shivank Garg , seanjc@google.com, vbabka@suse.cz, willy@infradead.org, akpm@linux-foundation.org, shuah@kernel.org, pbonzini@redhat.com, brauner@kernel.org, viro@zeniv.linux.org.uk Cc: ackerleytng@google.com, paul@paul-moore.com, jmorris@namei.org, serge@hallyn.com, pvorel@suse.cz, bfoster@redhat.com, tabba@google.com, vannapurve@google.com, chao.gao@intel.com, bharata@amd.com, nikunj@amd.com, michael.day@amd.com, shdhiman@amd.com, yan.y.zhao@intel.com, Neeraj.Upadhyay@amd.com, thomas.lendacky@amd.com, michael.roth@amd.com, aik@amd.com, jgg@nvidia.com, kalyazin@amazon.com, peterx@redhat.com, jack@suse.cz, rppt@kernel.org, hch@infradead.org, cgzones@googlemail.com, ira.weiny@intel.com, rientjes@google.com, roypat@amazon.co.uk, ziy@nvidia.com, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, gourry@gourry.net, kent.overstreet@linux.dev, ying.huang@linux.alibaba.com, apopple@nvidia.com, chao.p.peng@intel.com, amit@infradead.org, ddutile@redhat.com, dan.j.williams@intel.com, ashish.kalra@amd.com, gshan@redhat.com, jgowans@amazon.com, pankaj.gupta@amd.com, papaluri@amd.com, yuzhao@google.com, suzuki.poulose@arm.com, quic_eberman@quicinc.com, aneeshkumar.kizhakeveetil@arm.com, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-coco@lists.linux.dev References: <20250713174339.13981-2-shivankg@amd.com> <20250713174339.13981-4-shivankg@amd.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 13.07.25 19:43, Shivank Garg wrote: > From: Ackerley Tng > > guest_memfd's inode represents memory the guest_memfd is > providing. guest_memfd's file represents a struct kvm's view of that > memory. > > Using a custom inode allows customization of the inode teardown > process via callbacks. For example, ->evict_inode() allows > customization of the truncation process on file close, and > ->destroy_inode() and ->free_inode() allow customization of the inode > freeing process. > > Customizing the truncation process allows flexibility in management of > guest_memfd memory and customization of the inode freeing process > allows proper cleanup of memory metadata stored on the inode. > > Memory metadata is more appropriately stored on the inode (as opposed > to the file), since the metadata is for the memory and is not unique > to a specific binding and struct kvm. > > Co-developed-by: Fuad Tabba > Signed-off-by: Fuad Tabba > Signed-off-by: Ackerley Tng > Signed-off-by: Shivank Garg > --- [...] > > #include "kvm_mm.h" > > +static struct vfsmount *kvm_gmem_mnt; > + > struct kvm_gmem { > struct kvm *kvm; > struct xarray bindings; > @@ -388,9 +392,51 @@ static struct file_operations kvm_gmem_fops = { > .fallocate = kvm_gmem_fallocate, > }; > > -void kvm_gmem_init(struct module *module) > +static const struct super_operations kvm_gmem_super_operations = { > + .statfs = simple_statfs, > +}; > + > +static int kvm_gmem_init_fs_context(struct fs_context *fc) > +{ > + struct pseudo_fs_context *ctx; > + > + if (!init_pseudo(fc, GUEST_MEMFD_MAGIC)) > + return -ENOMEM; > + > + ctx = fc->fs_private; > + ctx->ops = &kvm_gmem_super_operations; Curious, why is that required? (secretmem doesn't have it, so I wonder) > + > + return 0; > +} > + > +static struct file_system_type kvm_gmem_fs = { > + .name = "kvm_guest_memory", It's GUEST_MEMFD_MAGIC but here "kvm_guest_memory". For secretmem it's SECRETMEM_MAGIC vs. "secretmem". So naturally, I wonder if that is to be made consistent :) > + .init_fs_context = kvm_gmem_init_fs_context, > + .kill_sb = kill_anon_super, > +}; > + > +static int kvm_gmem_init_mount(void) > +{ > + kvm_gmem_mnt = kern_mount(&kvm_gmem_fs); > + > + if (IS_ERR(kvm_gmem_mnt)) > + return PTR_ERR(kvm_gmem_mnt); > + > + kvm_gmem_mnt->mnt_flags |= MNT_NOEXEC; > + return 0; > +} > + > +int kvm_gmem_init(struct module *module) > { > kvm_gmem_fops.owner = module; > + > + return kvm_gmem_init_mount(); > +} > + > +void kvm_gmem_exit(void) > +{ > + kern_unmount(kvm_gmem_mnt); > + kvm_gmem_mnt = NULL; > } > > static int kvm_gmem_migrate_folio(struct address_space *mapping, > @@ -472,11 +518,71 @@ static const struct inode_operations kvm_gmem_iops = { > .setattr = kvm_gmem_setattr, > }; > > +static struct inode *kvm_gmem_inode_make_secure_inode(const char *name, > + loff_t size, u64 flags) > +{ > + struct inode *inode; > + > + inode = anon_inode_make_secure_inode(kvm_gmem_mnt->mnt_sb, name, NULL); > + if (IS_ERR(inode)) > + return inode; > + > + inode->i_private = (void *)(unsigned long)flags; > + inode->i_op = &kvm_gmem_iops; > + inode->i_mapping->a_ops = &kvm_gmem_aops; > + inode->i_mode |= S_IFREG; > + inode->i_size = size; > + mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER); > + mapping_set_inaccessible(inode->i_mapping); > + /* Unmovable mappings are supposed to be marked unevictable as well. */ > + WARN_ON_ONCE(!mapping_unevictable(inode->i_mapping)); > + > + return inode; > +} > + > +static struct file *kvm_gmem_inode_create_getfile(void *priv, loff_t size, > + u64 flags) > +{ > + static const char *name = "[kvm-gmem]"; > + struct inode *inode; > + struct file *file; > + int err; > + > + err = -ENOENT; > + if (!try_module_get(kvm_gmem_fops.owner)) > + goto err; Curious, shouldn't there be a module_put() somewhere after this function returned a file? > + > + inode = kvm_gmem_inode_make_secure_inode(name, size, flags); > + if (IS_ERR(inode)) { > + err = PTR_ERR(inode); > + goto err_put_module; > + } > + > + file = alloc_file_pseudo(inode, kvm_gmem_mnt, name, O_RDWR, > + &kvm_gmem_fops); > + if (IS_ERR(file)) { > + err = PTR_ERR(file); > + goto err_put_inode; > + } > + > + file->f_flags |= O_LARGEFILE; > + file->private_data = priv; > + > Nothing else jumped at me. -- Cheers, David / dhildenb