Re: [PATCH 1/3] drm/xe: Add a function to zap page table by address range

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

On Tue, 2025-01-28 at 17:21 -0500, Oak Zeng wrote:
> Add a function xe_pt_zap_range. This is similar to xe_pt_zap_ptes
> but is used when we don't have a vma to work with, such as zap
> a range mapped to scratch page where we don't have vma.
> 
> Signed-off-by: Oak Zeng <oak.zeng@intel.com>

As I think also Matt mentions, The zap functionality works only when it
exactly matches a pre-bound range (like in this case a vma) and there
is something cleaning up the zapped ptes afterwards. Typically that's a
rebind or an unbind.

Thanks,
Thomas



> ---
>  drivers/gpu/drm/xe/xe_pt.c | 28 ++++++++++++++++++++++++++++
>  drivers/gpu/drm/xe/xe_pt.h |  2 ++
>  2 files changed, 30 insertions(+)
> 
> diff --git a/drivers/gpu/drm/xe/xe_pt.c b/drivers/gpu/drm/xe/xe_pt.c
> index 1ddcc7e79a93..2363260da6a6 100644
> --- a/drivers/gpu/drm/xe/xe_pt.c
> +++ b/drivers/gpu/drm/xe/xe_pt.c
> @@ -792,6 +792,34 @@ static const struct xe_pt_walk_ops
> xe_pt_zap_ptes_ops = {
>  	.pt_entry = xe_pt_zap_ptes_entry,
>  };
>  
> +/**
> + * xe_pt_zap_range() - Zap (zero) gpu ptes of an virtual address
> range
> + * @tile: The tile we're zapping for.
> + * @vm: The vm we're zapping for.
> + * @start: Start of the virtual address range, inclusive.
> + * @end: End of the virtual address range, exclusive.
> + *
> + * This is similar to xe_pt_zap_ptes() but it's used when we don't
> have a
> + * vma to work with. This is used for example when we're clearing
> the scratch
> + * page mapping during vm_bind.
> + *
> + */
> +void xe_pt_zap_range(struct xe_tile *tile, struct xe_vm *vm, u64
> start, u64 end)
> +{
> +	struct xe_pt_zap_ptes_walk xe_walk = {
> +		.base = {
> +			.ops = &xe_pt_zap_ptes_ops,
> +			.shifts = xe_normal_pt_shifts,
> +			.max_level = XE_PT_HIGHEST_LEVEL,
> +		},
> +		.tile = tile,
> +	};
> +	struct xe_pt *pt = vm->pt_root[tile->id];
> +
> +	(void)xe_pt_walk_shared(&pt->base, pt->level, start,
> +				end, &xe_walk.base);
> +}
> +
>  /**
>   * xe_pt_zap_ptes() - Zap (zero) gpu ptes of an address range
>   * @tile: The tile we're zapping for.
> diff --git a/drivers/gpu/drm/xe/xe_pt.h b/drivers/gpu/drm/xe/xe_pt.h
> index 9ab386431cad..b166b324f455 100644
> --- a/drivers/gpu/drm/xe/xe_pt.h
> +++ b/drivers/gpu/drm/xe/xe_pt.h
> @@ -43,4 +43,6 @@ void xe_pt_update_ops_abort(struct xe_tile *tile,
> struct xe_vma_ops *vops);
>  
>  bool xe_pt_zap_ptes(struct xe_tile *tile, struct xe_vma *vma);
>  
> +void xe_pt_zap_range(struct xe_tile *tile, struct xe_vm *vm, u64
> start, u64 end);
> +
>  #endif