[Xen-devel] Re: [Xen-changelog] Work aroudn swiotlb issue where a read-only host buffer is

[Muli Ben-Yehuda <mulix@xxxxxxxxx>]

On Sat, Dec 17, 2005 at 12:28:06PM +0000, Xen patchbot -unstable wrote:
> # HG changeset patch
> # User kaf24@xxxxxxxxxxxxxxxxxxxx
> # Node ID b92ca87a2403d465e4d1087f8a7a43223b21bed8
> # Parent  1509521c824efbae25bb953a2e2a49ab3f7fe7f4
> Work aroudn swiotlb issue where a read-only host buffer is
> mapped for DMA_BIDIRECTIONAL streaming access by certain
> low-level drivers. This causes an unnecessary copy to the
> host buffer that previously caused a fatal kernel page fault.

The fix (calling __copy_to_user on a kernelspace buffer) seems rather
awkward, and will probably make tools such as sparse faint in
horror. Wouldn't it make more sense to have the buffer mapped
read/write in the first place and/or fix the LLDD to not do
DMA_BIDIRECTIONAL? (I don't know which of these is correct; I suspect
the second?)

Cheers,
Muli
-- 
Muli Ben-Yehuda
http://www.mulix.org | http://mulix.livejournal.com/


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