svn commit: r245147 - head/sys/arm/include

[Konstantin Belousov]

On Tue, Jan 08, 2013 at 02:40:20AM +0000, Oleksandr Tymoshenko wrote:
> Author: gonzo
> Date: Tue Jan  8 02:40:20 2013
> New Revision: 245147
> URL: http://svnweb.freebsd.org/changeset/base/245147
> 
> Log:
>   Switch default cache type for ARMv6/ARMv7 from write-through to
>   writeback-writeallocate
Could you, please, describe how this is supposed to work.

Assume that a process mapped the same file page at two different
addresses, both read-write, and writes to both mappings. Usermode code
does not consider the need to flush caches or synchronize writes into
non-overlapping regions, usually. Would it break, i.e. could the values
appear in the page which were never written to it ?

Another similar question, sf buffers on ARM flush the cache on sf_buf_free()
(sometimes). If the page, for which the sf buffer is created, mapped into
the userspace read-write, could it be that a value appears that was never
written ? Note that sf buffers are used e.g. by uiomove_fromphys().
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