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    SubjectRe: [patch] cache flush bug in mm/filemap.c (all kernels >= 2.5.30(at least))
    On Mon, May 26 2003, Russell King wrote:
    > On Sun, May 25, 2003 at 08:19:32PM -0700, David S. Miller wrote:
    > > Oh yes, this part is. If you don't ensure this, everything
    > > breaks.
    > >
    > > At the end of an I/O operation, say to a page cache page, that
    > > data ought to be visible equally to a userspace vs. a kernel
    > > space mapping to that page.
    > >
    > > For example, this is why we use language about "cpu visibility" in the
    > > DMA api documentation and not "kernel cpu visibility" :-) And because
    > > PIO transfers are basically pseudo-DMA they need to make the same exact
    > > guarentees.
    > >
    > > If you've been living in a world where you didn't think this is
    > > necessary, I certainly feel bad for you :-)
    >
    > Ok, so the flush_dcache_page() interface looses this; the original
    > placement of the flush_page_to_ram() ensured that data written by
    > device drivers was visible to user space.
    >
    > Maybe the BIO layer can handle this - the same problem exists when
    > (and if) BIO uses a bounce buffer, so it would have to be handled
    > there. Jens?

    For bouncing it's relatively trivial to add (and probably should, feel
    free...). PIO etc is really a driver problem to handle, I don't see how
    that could be handled generically.

    --
    Jens Axboe

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