[PATCH] drm/ttm: Restore ttm prefaulting

[Koenig, Christian]

Am 12.09.19 um 20:38 schrieb Thomas Hellström (VMware):
> 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>

Reviewed-by: Christian König <christian.koenig at amd.com>

Going to pick that up when Alex rebases our upstream branch.

Christian.

> ---
>   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))