From: David Hildenbrand <david@redhat.com>
To: Suren Baghdasaryan <surenb@google.com>, 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
Subject: Re: [PATCH v3 2/3] userfaultfd: UFFDIO_MOVE uABI
Date: Mon, 23 Oct 2023 14:29:34 +0200 [thread overview]
Message-ID: <721366d0-7909-45c9-ae49-f652c8369b9d@redhat.com> (raw)
In-Reply-To: <20231009064230.2952396-3-surenb@google.com>
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
next prev parent reply other threads:[~2023-10-23 12:29 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-09 6:42 [PATCH v3 0/3] userfaultfd move option Suren Baghdasaryan
2023-10-09 6:42 ` [PATCH v3 1/3] mm/rmap: support move to different root anon_vma in folio_move_anon_rmap() Suren Baghdasaryan
2023-10-12 22:01 ` Peter Xu
2023-10-13 8:04 ` David Hildenbrand
2023-10-19 15:19 ` Suren Baghdasaryan
2023-10-09 6:42 ` [PATCH v3 2/3] userfaultfd: UFFDIO_MOVE uABI Suren Baghdasaryan
2023-10-09 14:38 ` David Hildenbrand
2023-10-09 16:21 ` Suren Baghdasaryan
2023-10-09 16:23 ` David Hildenbrand
2023-10-09 16:29 ` Lokesh Gidra
2023-10-09 17:56 ` Lokesh Gidra
2023-10-10 1:49 ` Suren Baghdasaryan
2023-10-12 20:11 ` Peter Xu
2023-10-13 9:56 ` David Hildenbrand
2023-10-13 16:08 ` Peter Xu
2023-10-13 16:49 ` Lokesh Gidra
2023-10-13 17:05 ` Peter Xu
2023-10-16 18:01 ` David Hildenbrand
2023-10-16 19:01 ` Peter Xu
2023-10-17 15:55 ` David Hildenbrand
2023-10-17 18:59 ` Peter Xu
2023-10-19 15:41 ` David Hildenbrand
2023-10-19 19:53 ` Peter Xu
2023-10-19 20:02 ` Suren Baghdasaryan
2023-10-19 20:43 ` Peter Xu
2023-10-20 10:02 ` David Hildenbrand
2023-10-20 14:09 ` Suren Baghdasaryan
2023-10-20 17:16 ` David Hildenbrand
2023-10-22 15:46 ` Peter Xu
2023-10-23 12:03 ` David Hildenbrand
2023-10-23 16:36 ` David Hildenbrand
2023-10-23 17:33 ` Suren Baghdasaryan
2023-10-19 21:45 ` Suren Baghdasaryan
2023-10-12 21:59 ` Peter Xu
2023-10-19 21:24 ` Suren Baghdasaryan
2023-10-22 17:01 ` Peter Xu
2023-10-23 17:43 ` Suren Baghdasaryan
2023-10-23 18:37 ` Peter Xu
2023-10-23 19:01 ` Suren Baghdasaryan
2023-10-17 19:39 ` kernel test robot
2023-10-19 21:55 ` Suren Baghdasaryan
2023-10-23 12:29 ` David Hildenbrand [this message]
2023-10-23 15:53 ` David Hildenbrand
2023-10-23 19:00 ` Suren Baghdasaryan
2023-10-23 18:56 ` Suren Baghdasaryan
2023-10-24 14:27 ` David Hildenbrand
2023-10-24 14:36 ` Suren Baghdasaryan
2023-10-09 6:42 ` [PATCH v3 3/3] selftests/mm: add UFFDIO_MOVE ioctl test Suren Baghdasaryan
2023-10-12 22:29 ` Peter Xu
2023-10-19 15:43 ` Suren Baghdasaryan
2023-10-19 17:29 ` Axel Rasmussen
2023-10-19 19:33 ` Peter Xu
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