[PATCH 3/4] mm: simplify device private page handling in hmm_range_fault

[Christoph Hellwig]

On Mon, Mar 16, 2020 at 03:49:51PM -0700, Ralph Campbell wrote:
> On 3/16/20 12:32 PM, Christoph Hellwig wrote:
>> Remove the code to fault device private pages back into system memory
>> that has never been used by any driver.  Also replace the usage of the
>> HMM_PFN_DEVICE_PRIVATE flag in the pfns array with a simple
>> is_device_private_page check in nouveau.
>>
>> Signed-off-by: Christoph Hellwig <hch at lst.de>
>
> Getting rid of HMM_PFN_DEVICE_PRIVATE seems reasonable to me since a driver can
> look at the struct page but what if a driver needs to fault in a page from
> another device's private memory? Should it call handle_mm_fault()?

Obviously no driver cared for that so far.  Once we have test cases
for that and thus testable code we can add code to fault it in from
hmm_vma_handle_pte.