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[2003:cb:c738:1900:b6ea:5b9:62c0:34e]) by smtp.gmail.com with ESMTPSA id k12-20020a5d518c000000b0031f82743e25sm7659046wrv.67.2023.10.23.05.29.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 23 Oct 2023 05:29:36 -0700 (PDT) Message-ID: <721366d0-7909-45c9-ae49-f652c8369b9d@redhat.com> Date: Mon, 23 Oct 2023 14:29:34 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 2/3] userfaultfd: UFFDIO_MOVE uABI To: Suren Baghdasaryan , akpm@linux-foundation.org Cc: viro@zeniv.linux.org.uk, brauner@kernel.org, shuah@kernel.org, aarcange@redhat.com, lokeshgidra@google.com, peterx@redhat.com, hughd@google.com, mhocko@suse.com, axelrasmussen@google.com, rppt@kernel.org, willy@infradead.org, Liam.Howlett@oracle.com, jannh@google.com, zhangpeng362@huawei.com, bgeffon@google.com, kaleshsingh@google.com, ngeoffray@google.com, jdduke@google.com, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, kernel-team@android.com References: <20231009064230.2952396-1-surenb@google.com> <20231009064230.2952396-3-surenb@google.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 41E721C002C X-Stat-Signature: qopj7hun6s5jsikrs943ttzu75xaq16s X-HE-Tag: 1698064180-434329 X-HE-Meta: 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 ZdrEAxRK QWLbr63QD/i1GjFOyQhu/5XrZXW66o7nqVOKlSlQ4sTfbVLk0YonpKcJl0QzUZvKZf85mvOF1WJoYxuC99mBFnpFNIY6JqVbLnb7cn9iW/nOjG8HSfNS7ToGQHCkpCppiyerlXgLDdI3Z3NiSozylYSzNXLeZG5VujYuc6Q3qT8I3dvSMCAjR7nsDIDd8mkJzSxd72uHgCzJ8Ven9BrDvJB3hKU303C4FHdFb+4xbFxZ8Bhp9reSuxJo9+be/YwUVbafzbtgYMgzkcVtG5mq/lv/g+ilLMKt87DF/sPwb02EYZBHc2Oz+MHODgmNFS6Wt0wGHOT3ozYBjwdocOU1CroQ4A0AsZKBt0LUUynRXVfILxvBxmHQj1TNZE0QACdqTarRt1Bv9oxgOLo6tIMVem7WJLhRE1OB/ylGZufXCQzYxw4Z1F69h95LHJ/mlD23yDbgiAZh5gsUkA1I/SODyAj2Ssg== 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: Focusing on validate_remap_areas(): > + > +static int validate_remap_areas(struct vm_area_struct *src_vma, > + struct vm_area_struct *dst_vma) > +{ > + /* Only allow remapping if both have the same access and protection */ > + if ((src_vma->vm_flags & VM_ACCESS_FLAGS) != (dst_vma->vm_flags & VM_ACCESS_FLAGS) || > + pgprot_val(src_vma->vm_page_prot) != pgprot_val(dst_vma->vm_page_prot)) > + return -EINVAL; Makes sense. I do wonder about pkey and friends and if we even have to so anything special. > + > + /* Only allow remapping if both are mlocked or both aren't */ > + if ((src_vma->vm_flags & VM_LOCKED) != (dst_vma->vm_flags & VM_LOCKED)) > + return -EINVAL; > + > + if (!(src_vma->vm_flags & VM_WRITE) || !(dst_vma->vm_flags & VM_WRITE)) > + return -EINVAL; Why does one of both need VM_WRITE? If one really needs it, then the destination (where we're moving stuff to). > + > + /* > + * Be strict and only allow remap_pages if either the src or > + * dst range is registered in the userfaultfd to prevent > + * userland errors going unnoticed. As far as the VM > + * consistency is concerned, it would be perfectly safe to > + * remove this check, but there's no useful usage for > + * remap_pages ouside of userfaultfd registered ranges. This > + * is after all why it is an ioctl belonging to the > + * userfaultfd and not a syscall. I think the last sentence is the important bit and the comment can likely be reduced. > + * > + * Allow both vmas to be registered in the userfaultfd, just > + * in case somebody finds a way to make such a case useful. > + * Normally only one of the two vmas would be registered in > + * the userfaultfd. Should we just check the destination? That makes most sense to me, because with uffd we are resolving uffd-events. And just like copy/zeropage we want to resolve a page fault ("userfault") of a non-present page on the destination. > + */ > + if (!dst_vma->vm_userfaultfd_ctx.ctx && > + !src_vma->vm_userfaultfd_ctx.ctx) > + return -EINVAL; > + > + /* > + * FIXME: only allow remapping across anonymous vmas, > + * tmpfs should be added. > + */ > + if (!vma_is_anonymous(src_vma) || !vma_is_anonymous(dst_vma)) > + return -EINVAL; Why a FIXME here? Just drop the comment completely or replace it with "We only allow to remap anonymous folios accross anonymous VMAs". > + > + /* > + * Ensure the dst_vma has a anon_vma or this page > + * would get a NULL anon_vma when moved in the > + * dst_vma. > + */ > + if (unlikely(anon_vma_prepare(dst_vma))) > + return -ENOMEM; Makes sense. > + > + return 0; > +} -- Cheers, David / dhildenb