From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Dan Williams <dan.j.williams@intel.com>
Cc: darrick.wong@oracle.com, Jan Kara <jack@suse.cz>,
linux-nvdimm@lists.01.org, linux-api@vger.kernel.org,
Dave Chinner <david@fromorbit.com>,
linux-kernel@vger.kernel.org, linux-xfs@vger.kernel.org,
linux-mm@kvack.org, Jeff Moyer <jmoyer@redhat.com>,
Alexander Viro <viro@zeniv.linux.org.uk>,
luto@kernel.org, linux-fsdevel@vger.kernel.org,
Ross Zwisler <ross.zwisler@linux.intel.com>,
Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH v4 3/3] fs, xfs: introduce MAP_DIRECT for creating block-map-sealed file ranges
Date: Tue, 15 Aug 2017 12:18:36 +0300 [thread overview]
Message-ID: <20170815091836.c3xpsfgfwz7w35od@node.shutemov.name> (raw)
In-Reply-To: <150277754211.23945.458876600578531019.stgit@dwillia2-desk3.amr.corp.intel.com>
On Mon, Aug 14, 2017 at 11:12:22PM -0700, Dan Williams wrote:
> MAP_DIRECT is an mmap(2) flag with the following semantics:
>
> MAP_DIRECT
> In addition to this mapping having MAP_SHARED semantics, successful
> faults in this range may assume that the block map (logical-file-offset
> to physical memory address) is pinned for the lifetime of the mapping.
> Successful MAP_DIRECT faults establish mappings that bypass any kernel
> indirections like the page-cache. All updates are carried directly
> through to the underlying file physical blocks (modulo cpu cache
> effects).
>
> ETXTBSY is returned on attempts to change the block map (allocate blocks
> / convert unwritten extents / break shared extents) in the mapped range.
> Some filesystems may extend these same restrictions outside the mapped
> range and return ETXTBSY to any file operations that might mutate the
> block map. MAP_DIRECT faults may fail with a SIGSEGV if the filesystem
> needs to write the block map to satisfy the fault. For example, if the
> mapping was established over a hole in a sparse file.
We had issues before with user-imposed ETXTBSY. See MAP_DENYWRITE.
Are we sure it won't a source of denial-of-service attacks?
> The kernel ignores attempts to mark a MAP_DIRECT mapping MAP_PRIVATE and
> will silently fall back to MAP_SHARED semantics.
Hm.. Any reason for this strage behaviour? Looks just broken to me.
>
> ERRORS
> EACCES A MAP_DIRECT mapping was requested and PROT_WRITE was not set.
>
> EINVAL MAP_ANONYMOUS was specified with MAP_DIRECT.
>
> EOPNOTSUPP The filesystem explicitly does not support the flag
>
> SIGSEGV Attempted to write a MAP_DIRECT mapping at a file offset that
> might require block-map updates.
I think it should be SIGBUS.
--
Kirill A. Shutemov
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next prev parent reply other threads:[~2017-08-15 9:18 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-15 6:12 [PATCH v4 0/3] MAP_DIRECT and block-map sealed files Dan Williams
2017-08-15 6:12 ` [PATCH v4 1/3] fs, xfs: introduce S_IOMAP_SEALED Dan Williams
[not found] ` <150277752553.23945.13932394738552748440.stgit-p8uTFz9XbKj2zm6wflaqv1nYeNYlB/vhral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2017-08-15 6:12 ` [PATCH v4 2/3] mm: introduce MAP_VALIDATE a mechanism for adding new mmap flags Dan Williams
2017-08-15 12:27 ` Jan Kara
[not found] ` <20170815122701.GF27505-4I4JzKEfoa/jFM9bn6wA6Q@public.gmane.org>
2017-08-15 16:24 ` Dan Williams
2017-09-17 3:44 ` Dan Williams
[not found] ` <CAA9_cmc0vejxCsc1NWp5b4C0CSsO5xetF3t6LCoCuEYB6yPiwQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-09-17 17:39 ` Christoph Hellwig
[not found] ` <20170917173945.GA22200-jcswGhMUV9g@public.gmane.org>
2017-09-18 9:31 ` Jan Kara
2017-09-18 15:47 ` Dan Williams
2017-09-18 9:26 ` Jan Kara
2017-08-15 16:28 ` Andy Lutomirski
2017-08-15 22:31 ` Dan Williams
2017-08-17 8:06 ` kbuild test robot
2017-08-15 6:12 ` [PATCH v4 3/3] fs, xfs: introduce MAP_DIRECT for creating block-map-sealed file ranges Dan Williams
2017-08-15 9:18 ` Kirill A. Shutemov [this message]
2017-08-15 17:11 ` Dan Williams
2017-08-16 10:25 ` Kirill A. Shutemov
[not found] ` <150277754211.23945.458876600578531019.stgit-p8uTFz9XbKj2zm6wflaqv1nYeNYlB/vhral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2017-08-15 12:42 ` Jan Kara
[not found] ` <20170815124250.GG27505-4I4JzKEfoa/jFM9bn6wA6Q@public.gmane.org>
2017-08-15 16:29 ` Dan Williams
[not found] ` <CAPcyv4h01os0Gc6bYmaGdMXt5q4G4zfirNRPWG3=gQi5POrpmg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-08-16 1:15 ` Dan Williams
2017-08-17 8:49 ` kbuild test robot
2017-08-15 9:01 ` [PATCH v4 0/3] MAP_DIRECT and block-map sealed files Dave Chinner
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