lkml.org 
[lkml]   [2013]   [Nov]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    SubjectRe: [PATCH] aio: fix D-cache aliasing issues
    Date
    On 16-Nov-13, at 5:37 PM, James Bottomley wrote:

    > On Sat, 2013-11-16 at 17:32 -0500, John David Anglin wrote:
    >> On 16-Nov-13, at 5:06 PM, James Bottomley wrote:
    >>
    >>> On Sat, 2013-11-16 at 21:07 +0100, Simon Baatz wrote:
    >>>> On Fri, Nov 15, 2013 at 02:42:05PM -0800, James Bottomley wrote:
    >>>>> On Fri, 2013-11-15 at 23:05 +0100, Helge Deller wrote:
    >>>>>> When a user page mapping is released via kunmap*() functions, the
    >>>>>> D-cache needs
    >>>>>> to be flushed via flush_dcache_page() to avoid D-cache aliasing
    >>>>>> issues.
    >>>>>>
    >>>>>> This patch fixes aio on the parisc platform (and probably
    >>>>>> others).
    >>>>>
    >>>>> This should be flush_kernel_dcache_page(). flush_dcache_page() is
    >>>>> for
    >>>>> full coherency but for unmap, we know the page was coherent going
    >>>>> in and
    >>>>> may have been modified by the kernel, so only the kernel view
    >>>>> needs to
    >>>>> be sync'd. Technically, by the kernel API, the flush should be
    >>>>> done
    >>>>> *before* unmapping. This would have mattered on parisc until we
    >>>>> did
    >>>>> flush via tmpalias which means we no-longer care if the mapping
    >>>>> for the
    >>>>> flush exists or not because we always recreate it via the tmpalias
    >>>>> pages.
    >>>>
    >>>> On ARM, flush_kernel_dcache_page() actually assumes that the page
    >>>> is
    >>>> mapped. It avoids double flushing of highmem pages by not flushing
    >>>> in those cases where kunmap_atomic() already takes care of
    >>>> flushing.
    >>>
    >>> On Parisc, kmap/kunmap is currently a nop. However, if we ever
    >>> implemented highmem, we would also need to flush before we unmap,
    >>> which
    >>> is why the flush needs to go before the kunmap.
    >>
    >> Not quite. On PA8800/PA8900, we currently do a flush in kunmap.
    >>
    >> I'm fairly certain from discussion with Helge that he saw this bug on
    >> a C8000
    >> with PA8800 processor. In that case, adding a call to
    >> flush_kernel_dcache_page()
    >> just duplicates the call in kunmap().
    >
    > Yes, if that's true it won't be the solution.

    The calls may be needed for the two cases where the page is changed,
    but I don't
    know how to avoid double flush on PA8800/PA8900 without changing the
    primatives.

    Dave
    --
    John David Anglin dave.anglin@bell.net





    \
     
     \ /
      Last update: 2013-11-17 00:21    [W:5.820 / U:0.068 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site