[Intel-gfx] [PATCH 4/4] i915: fix remap_io_sg to verify the pgprot

[Thomas Hellström]

On 5/18/21 3:23 PM, Christoph Hellwig wrote:
> On Mon, May 17, 2021 at 11:46:35PM +0200, Thomas Hellström wrote:
>> Apart from the caching aliasing Mattew brought up, doesn't the
>> remap_pfn_range_xxx() family require the mmap_sem held in write mode since
>> it modifies the vma structure? remap_io_sg() is called from the fault
>> handler with the mmap_sem held in read mode only.
> Only for vma->vm_flags, and remap_sg already asserts all the interesting
> flags are set, although it does not assert VM_IO.
>
> We could move the assignment out of remap_pfn_range_notrack and
> into remap_pfn_range and just assert that the proper flags are set,
> though.

That to me sounds like a way forward. It sound like in general a gpu 
prefaulting helper that in the long run also supports faulting huge ptes 
is desired also by TTM. Although it looks like that BUG_ON() I pointed 
out was hit anyway....

/Thomas