[PATCH] drm/ttm: Restore ttm prefaulting

[Souptick Joarder]

On Fri, Sep 13, 2019 at 12:09 AM Thomas Hellström (VMware)
<thomas_os at shipmail.org> wrote:
>
> From: Thomas Hellstrom <thellstrom at vmware.com>
>
> Commit 4daa4fba3a38 ("gpu: drm: ttm: Adding new return type vm_fault_t")
> broke TTM prefaulting. Since vmf_insert_mixed() typically always returns
> VM_FAULT_NOPAGE, prefaulting stops after the second PTE.
>
> Restore (almost) the original behaviour. Unfortunately we can no longer
> with the new vm_fault_t return type determine whether a prefaulting
> PTE insertion hit an already populated PTE, and terminate the insertion
> loop. Instead we continue with the pre-determined number of prefaults.
>
> Fixes: 4daa4fba3a38 ("gpu: drm: ttm: Adding new return type vm_fault_t")
> Cc: Souptick Joarder <jrdr.linux at gmail.com>
> Cc: Christian König <christian.koenig at amd.com>
> Signed-off-by: Thomas Hellstrom <thellstrom at vmware.com>

This commit merged into 4.19. Need to Cc stable.

Cc: stable at vger.kernel.org # v4.19+

> ---
>  drivers/gpu/drm/ttm/ttm_bo_vm.c | 16 +++++++---------
>  1 file changed, 7 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> index 5a580adeb9d1..aa18e8a53727 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> @@ -290,15 +290,13 @@ vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf,
>                 else
>                         ret = vmf_insert_pfn(&cvma, address, pfn);
>
> -               /*
> -                * Somebody beat us to this PTE or prefaulting to
> -                * an already populated PTE, or prefaulting error.
> -                */
> -
> -               if (unlikely((ret == VM_FAULT_NOPAGE && i > 0)))
> -                       break;
> -               else if (unlikely(ret & VM_FAULT_ERROR))
> -                       goto out_io_unlock;
> +               /* Never error on prefaulted PTEs */
> +               if (unlikely((ret & VM_FAULT_ERROR))) {
> +                       if (i == 0)
> +                               goto out_io_unlock;
> +                       else
> +                               break;
> +               }
>
>                 address += PAGE_SIZE;
>                 if (unlikely(++page_offset >= page_last))
> --
> 2.20.1
>