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Thu, 23 Jan 2025 20:26:18 -0800 (PST) X-Google-Smtp-Source: AGHT+IHF0DJWclieG8GIGsCzjY2k/MI/u8GaqIVA2CIVqY1sh8z4aaIMUWu09AlsDTA/tx+z6nHtoQ== X-Received: by 2002:a17:90b:4d05:b0:2ee:5958:828 with SMTP id 98e67ed59e1d1-2f782c70176mr42890346a91.9.1737692777958; Thu, 23 Jan 2025 20:26:17 -0800 (PST) Received: from [192.168.68.55] ([180.233.125.64]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-2f7ffa5bbfbsm591962a91.19.2025.01.23.20.25.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 23 Jan 2025 20:26:16 -0800 (PST) Message-ID: <186047ea-a782-494b-bfcf-f5088806bbb4@redhat.com> Date: Fri, 24 Jan 2025 14:25:56 +1000 Precedence: bulk X-Mailing-List: linux-arm-msm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v5 02/15] KVM: guest_memfd: Make guest mem use guest mem inodes instead of anonymous inodes To: Fuad Tabba , kvm@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-mm@kvack.org 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, yu.c.zhang@linux.intel.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 References: <20250117163001.2326672-1-tabba@google.com> <20250117163001.2326672-3-tabba@google.com> Content-Language: en-US From: Gavin Shan In-Reply-To: <20250117163001.2326672-3-tabba@google.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Hi Fuad, On 1/18/25 2:29 AM, Fuad Tabba wrote: > From: Ackerley Tng > > Using guest mem inodes allows us to store metadata for the backing > memory on the inode. Metadata will be added in a later patch to > support HugeTLB pages. > > Metadata about backing memory should not be stored on the file, since > the file represents a guest_memfd's binding with a struct kvm, and > metadata about backing memory is not unique to a specific binding and > struct kvm. > > Signed-off-by: Ackerley Tng > Signed-off-by: Fuad Tabba > --- > include/uapi/linux/magic.h | 1 + > virt/kvm/guest_memfd.c | 119 ++++++++++++++++++++++++++++++------- > 2 files changed, 100 insertions(+), 20 deletions(-) > > diff --git a/include/uapi/linux/magic.h b/include/uapi/linux/magic.h > index bb575f3ab45e..169dba2a6920 100644 > --- a/include/uapi/linux/magic.h > +++ b/include/uapi/linux/magic.h > @@ -103,5 +103,6 @@ > #define DEVMEM_MAGIC 0x454d444d /* "DMEM" */ > #define SECRETMEM_MAGIC 0x5345434d /* "SECM" */ > #define PID_FS_MAGIC 0x50494446 /* "PIDF" */ > +#define GUEST_MEMORY_MAGIC 0x474d454d /* "GMEM" */ > > #endif /* __LINUX_MAGIC_H__ */ > diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c > index 47a9f68f7b24..198554b1f0b5 100644 > --- a/virt/kvm/guest_memfd.c > +++ b/virt/kvm/guest_memfd.c > @@ -1,12 +1,17 @@ > // SPDX-License-Identifier: GPL-2.0 > +#include > +#include This can be dropped since "linux/mount.h" has been included to "linux/fs.h". > #include > #include > #include > +#include > #include > #include > > #include "kvm_mm.h" > > +static struct vfsmount *kvm_gmem_mnt; > + > struct kvm_gmem { > struct kvm *kvm; > struct xarray bindings; > @@ -307,6 +312,38 @@ static pgoff_t kvm_gmem_get_index(struct kvm_memory_slot *slot, gfn_t gfn) > return gfn - slot->base_gfn + slot->gmem.pgoff; > } > > +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_MEMORY_MAGIC)) > + return -ENOMEM; > + > + ctx = fc->fs_private; > + ctx->ops = &kvm_gmem_super_operations; > + > + return 0; > +} > + > +static struct file_system_type kvm_gmem_fs = { > + .name = "kvm_guest_memory", > + .init_fs_context = kvm_gmem_init_fs_context, > + .kill_sb = kill_anon_super, > +}; > + > +static void kvm_gmem_init_mount(void) > +{ > + kvm_gmem_mnt = kern_mount(&kvm_gmem_fs); > + BUG_ON(IS_ERR(kvm_gmem_mnt)); > + > + /* For giggles. Userspace can never map this anyways. */ > + kvm_gmem_mnt->mnt_flags |= MNT_NOEXEC; > +} > + > static struct file_operations kvm_gmem_fops = { > .open = generic_file_open, > .release = kvm_gmem_release, > @@ -316,6 +353,8 @@ static struct file_operations kvm_gmem_fops = { > void kvm_gmem_init(struct module *module) > { > kvm_gmem_fops.owner = module; > + > + kvm_gmem_init_mount(); > } > > static int kvm_gmem_migrate_folio(struct address_space *mapping, > @@ -397,11 +436,67 @@ 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) > +{ > + const struct qstr qname = QSTR_INIT(name, strlen(name)); > + struct inode *inode; > + int err; > + > + inode = alloc_anon_inode(kvm_gmem_mnt->mnt_sb); > + if (IS_ERR(inode)) > + return inode; > + > + err = security_inode_init_security_anon(inode, &qname, NULL); > + if (err) { > + iput(inode); > + return ERR_PTR(err); > + } > + > + 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; > + > + if (kvm_gmem_fops.owner && !try_module_get(kvm_gmem_fops.owner)) > + return ERR_PTR(-ENOENT); > + The validation on 'kvm_gmem_fops.owner' can be removed since try_module_get() and module_put() are friendly to a NULL parameter, even when CONFIG_MODULE_UNLOAD == N A module_put(kvm_gmem_fops.owner) is needed in the various erroneous cases in this function. Otherwise, the reference count of the owner (module) will become imbalanced on any errors. > + inode = kvm_gmem_inode_make_secure_inode(name, size, flags); > + if (IS_ERR(inode)) > + return ERR_CAST(inode); > + ERR_CAST may be dropped since there is nothing to be casted or converted? > + file = alloc_file_pseudo(inode, kvm_gmem_mnt, name, O_RDWR, > + &kvm_gmem_fops); > + if (IS_ERR(file)) { > + iput(inode); > + return file; > + } > + > + file->f_mapping = inode->i_mapping; > + file->f_flags |= O_LARGEFILE; > + file->private_data = priv; > + 'file->f_mapping = inode->i_mapping' may be dropped since it's already correctly set by alloc_file_pseudo(). alloc_file_pseudo alloc_path_pseudo alloc_file alloc_empty_file file_init_path // Set by this function > + return file; > +} > + > static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags) > { > - const char *anon_name = "[kvm-gmem]"; > struct kvm_gmem *gmem; > - struct inode *inode; > struct file *file; > int fd, err; > > @@ -415,32 +510,16 @@ static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags) > goto err_fd; > } > > - file = anon_inode_create_getfile(anon_name, &kvm_gmem_fops, gmem, > - O_RDWR, NULL); > + file = kvm_gmem_inode_create_getfile(gmem, size, flags); > if (IS_ERR(file)) { > err = PTR_ERR(file); > goto err_gmem; > } > > - file->f_flags |= O_LARGEFILE; > - > - inode = file->f_inode; > - WARN_ON(file->f_mapping != inode->i_mapping); > - > - 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)); > - > kvm_get_kvm(kvm); > gmem->kvm = kvm; > xa_init(&gmem->bindings); > - list_add(&gmem->entry, &inode->i_mapping->i_private_list); > + list_add(&gmem->entry, &file_inode(file)->i_mapping->i_private_list); > > fd_install(fd, file); > return fd; Thanks, Gavin