Re: [PATCH v3 4/6] drm/xe: Use ttm_bo_access in xe_vm_snapshot_capture_delayed

[Matthew Auld <matthew.auld@xxxxxxxxx>]

On 19/10/2024 20:20, Matthew Brost wrote:
> Non-contiguous mapping of BO in VRAM doesn't work, use ttm_bo_access
> instead.
>
> v2:
>   - Fix error handling
>
> Fixes: 0eb2a18a8fad ("drm/xe: Implement VM snapshot support for BO's and userptr")
> Suggested-by: Matthew Auld <matthew.auld@xxxxxxxxx>
> Signed-off-by: Matthew Brost <matthew.brost@xxxxxxxxx>

The other user looks to be the clear color stuff for display. See 
intel_bo_read_from_page(). I think that is also potentially busted?

> ---
>   drivers/gpu/drm/xe/xe_vm.c | 17 ++++++-----------
>   1 file changed, 6 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
> index c99380271de6..c8782da3a5c3 100644
> --- a/drivers/gpu/drm/xe/xe_vm.c
> +++ b/drivers/gpu/drm/xe/xe_vm.c
> @@ -3303,7 +3303,6 @@ void xe_vm_snapshot_capture_delayed(struct xe_vm_snapshot *snap)
>   
>   	for (int i = 0; i < snap->num_snaps; i++) {
>   		struct xe_bo *bo = snap->snap[i].bo;
> -		struct iosys_map src;
>   		int err;
>   
>   		if (IS_ERR(snap->snap[i].data))
> @@ -3316,16 +3315,12 @@ void xe_vm_snapshot_capture_delayed(struct xe_vm_snapshot *snap)
>   		}
>   
>   		if (bo) {
> -			xe_bo_lock(bo, false);

I think we still need the lock, or is that grabbed somewhere else? Also 
I guess CI doesn't currently hit this path?

> -			err = ttm_bo_vmap(&bo->ttm, &src);
> -			if (!err) {
> -				xe_map_memcpy_from(xe_bo_device(bo),
> -						   snap->snap[i].data,
> -						   &src, snap->snap[i].bo_ofs,
> -						   snap->snap[i].len);
> -				ttm_bo_vunmap(&bo->ttm, &src);
> -			}
> -			xe_bo_unlock(bo);
> +			err = ttm_bo_access(&bo->ttm, snap->snap[i].bo_ofs,
> +					    snap->snap[i].data, snap->snap[i].len, 0);
> +			if (!(err < 0) && err != snap->snap[i].len)
> +				err = -EIO;
> +			else if (!(err < 0))
> +				err = 0;
>   		} else {
>   			void __user *userptr = (void __user *)(size_t)snap->snap[i].bo_ofs;
>