Nick Piggin wrote:
On Wed, Oct 11, 2006 at 12:12:19PM +0200, Thomas Hellstrom wrote:
Nick, I just realized: would it be possible to have a pgprot_t argument
to this one, instead of it using vma->vm_pgprot?
The motivation for this (DRM again) is that some architectures (powerpc)
cannot map the AGP aperture through IO space, but needs to remap the
page from memory with a nocache attribute set. Others need special
pgprot settings for write-combined mappings.
Now, there's a possibility to change vma->vm_pgprot during the first
->fault(), but again, we only have the mmap_sem in read mode.
I don't see a problem with that. It would be nice if vm_pgprot could
be kept in synch with the pte protections, but I guess a crazy
driver should be allowed to do anything it wants ;)
:).
Actually, the caching bits are sort of left out from the mm code anyway.
For example, mprotect will reset them, which is sort of a security risc,
since an unpriviliged user can call mprotect on uncached page mappings,
causing inconsistent mappings and stability problems.
Thomas
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