Re: Calculating kernel logical address ..

Andrew Morton
2002-09-09T21:43:05Z

Manfred Spraul wrote:
>
> Andrew Morton wrote:
> > Nobody seems to have come forth to implement a thought-out scatter/gather,
> > map-user-pages library infrastructure so I'd be a bit reluctant to
> > break stuff without offering a replacement.
> >
>
> We'd need one.
>
> get_user_pages() is broken if a kernel module access the virtual address
> of the page and the cpu caches are not coherent:

OK. Most users seem to just want to put the pages under DMA though.

> Most of the flush functions need the vma pointer, but it's impossible to
> guarantee that it still exists when the get_user_pages() user calls
> page_cache_release().

Well presumably, if the driver is altering user memory by hand,
it is synchronous and they can hang onto mmap_sem while doing it?