Re: [PATCH v2 09/18] drm/via: set FOLL_PIN via pin_user_pages_fast()

[John Hubbard]

On 11/4/19 9:44 AM, Jerome Glisse wrote:
> On Sun, Nov 03, 2019 at 01:18:04PM -0800, John Hubbard wrote:
>> Convert drm/via to use the new pin_user_pages_fast() call, which sets
>> FOLL_PIN. Setting FOLL_PIN is now required for code that requires
>> tracking of pinned pages, and therefore for any code that calls
>> put_user_page().
>>
>> Reviewed-by: Ira Weiny <ira.weiny@xxxxxxxxx>
>> Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx>
> 
> Please be more explicit that via_dmablit.c is already using put_user_page()
> as i am expecting that any conversion to pin_user_pages*() must be pair with
> a put_user_page(). I find above commit message bit unclear from that POV.
> 

OK. This one, and the fs/io_uring (patch 9) and net/xdp (patch 10) were all
cases that had put_user_page() pre-existing. I will add something like the 
following to each commit description, for v3:

In partial anticipation of this work, the drm/via driver was already 
calling put_user_page() instead of put_page(). Therefore, in order to
convert from the get_user_pages()/put_page() model, to the
pin_user_pages()/put_user_page() model, the only change required
is to change get_user_pages() to pin_user_pages().

thanks,

John Hubbard
NVIDIA

> Reviewed-by: Jérôme Glisse <jglisse@xxxxxxxxxx>
> 
> 
>> ---
>>  drivers/gpu/drm/via/via_dmablit.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/via/via_dmablit.c b/drivers/gpu/drm/via/via_dmablit.c
>> index 3db000aacd26..37c5e572993a 100644
>> --- a/drivers/gpu/drm/via/via_dmablit.c
>> +++ b/drivers/gpu/drm/via/via_dmablit.c
>> @@ -239,7 +239,7 @@ via_lock_all_dma_pages(drm_via_sg_info_t *vsg,  drm_via_dmablit_t *xfer)
>>  	vsg->pages = vzalloc(array_size(sizeof(struct page *), vsg->num_pages));
>>  	if (NULL == vsg->pages)
>>  		return -ENOMEM;
>> -	ret = get_user_pages_fast((unsigned long)xfer->mem_addr,
>> +	ret = pin_user_pages_fast((unsigned long)xfer->mem_addr,
>>  			vsg->num_pages,
>>  			vsg->direction == DMA_FROM_DEVICE ? FOLL_WRITE : 0,
>>  			vsg->pages);
>> -- 
>> 2.23.0
>>
> 
>