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[2003:d8:2f3f:f800:c101:5c9f:3bc9:3d08]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-46e33b562d8sm31593705e9.0.2025.09.25.04.55.26 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 25 Sep 2025 04:55:29 -0700 (PDT) Message-ID: Date: Thu, 25 Sep 2025 13:55:26 +0200 Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH kvm-next V11 4/7] KVM: guest_memfd: Use guest mem inodes instead of anonymous inodes To: "Garg, Shivank" , Sean Christopherson , Ackerley Tng Cc: willy@infradead.org, akpm@linux-foundation.org, pbonzini@redhat.com, shuah@kernel.org, vbabka@suse.cz, brauner@kernel.org, viro@zeniv.linux.org.uk, dsterba@suse.com, xiang@kernel.org, chao@kernel.org, jaegeuk@kernel.org, clm@fb.com, josef@toxicpanda.com, kent.overstreet@linux.dev, zbestahu@gmail.com, jefflexu@linux.alibaba.com, dhavale@google.com, lihongbo22@huawei.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, rppt@kernel.org, surenb@google.com, mhocko@suse.com, ziy@nvidia.com, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, gourry@gourry.net, ying.huang@linux.alibaba.com, apopple@nvidia.com, tabba@google.com, paul@paul-moore.com, jmorris@namei.org, serge@hallyn.com, pvorel@suse.cz, bfoster@redhat.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, hch@infradead.org, cgzones@googlemail.com, ira.weiny@intel.com, rientjes@google.com, roypat@amazon.co.uk, 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, linux-bcachefs@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-erofs@lists.ozlabs.org, linux-f2fs-devel@lists.sourceforge.net, 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: <20250827175247.83322-2-shivankg@amd.com> <20250827175247.83322-7-shivankg@amd.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 25.09.25 13:44, Garg, Shivank wrote: > > > On 9/25/2025 8:20 AM, Sean Christopherson wrote: >> My apologies for the super late feedback. None of this is critical (mechanical >> things that can be cleaned up after the fact), so if there's any urgency to >> getting this series into 6.18, just ignore it. >> >> On Wed, Aug 27, 2025, Ackerley Tng wrote: >>> Shivank Garg writes: >>> @@ -463,11 +502,70 @@ bool __weak kvm_arch_supports_gmem_mmap(struct kvm *kvm) >>> return true; >>> } >>> >>> +static struct inode *kvm_gmem_inode_create(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; >>> + /* __fput() will take care of fops_put(). */ >>> + if (!fops_get(&kvm_gmem_fops)) >>> + goto err; >>> + >>> + inode = kvm_gmem_inode_create(name, size, flags); >>> + if (IS_ERR(inode)) { >>> + err = PTR_ERR(inode); >>> + goto err_fops_put; >>> + } >>> + >>> + 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; >>> + >>> + return file; >>> + >>> +err_put_inode: >>> + iput(inode); >>> +err_fops_put: >>> + fops_put(&kvm_gmem_fops); >>> +err: >>> + return ERR_PTR(err); >>> +} >> >> I don't see any reason to add two helpers. It requires quite a bit more lines >> of code due to adding more error paths and local variables, and IMO doesn't make >> the code any easier to read. >> >> Passing in "gmem" as @priv is especially ridiculous, as it adds code and >> obfuscates what file->private_data is set to. >> >> I get the sense that the code was written to be a "replacement" for common APIs, >> but that is nonsensical (no pun intended). >> >>> 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; >>> >>> @@ -481,32 +579,16 @@ 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); >> >> I don't understand this change? Isn't file_inode(file) == inode? >> >> Compile tested only, and again not critical, but it's -40 LoC... >> >> > > Thanks. > I did functional testing and it works fine. I can queue this instead. I guess I can reuse the patch description and add Sean as author + add his SOB (if he agrees). Let me take a look at the patch later in more detail. -- Cheers David / dhildenb