Re: [PATCH v5 06/11] drm/gpuvm: Add DRM_GPUVA_REPEAT flag and logic

[Danilo Krummrich]

On Fri Mar 13, 2026 at 4:09 PM CET, Adrián Larumbe wrote:
> From: Asahi Lina <lina+kernel@xxxxxxxxxxxxx>
>
> To be able to support "fake sparse" mappings without relying on GPU page
> fault handling, drivers may need to create large (e.g. 4GiB) mappings of
> the same page repeatedly (or same range of pages). Doing this through
> individual mappings would be very wasteful. This can be handled better
> by using a flag on map creation, but to do it safely, drm_gpuvm needs to
> be aware of this special case.
>
> Add a flag that signals that a given mapping is a page mapping, which is
> repeated all over the entire requested VA range. This tweaks the
> sm_map() logic to treat the GEM offsets differently when mappings are
> a repeated ones so they are not incremented as they would be with regular
> mappings.
>
> The size of the GEM portion to repeat is passed through
> drm_gpuva::gem::range. Most of the time it will be a page size, but
> it can be bigger as long as it's less than drm_gpuva::va::range, and
> drm_gpuva::va::range is a multiple of drm_gpuva::gem::range.
>
> Signed-off-by: Asahi Lina <lina+kernel@xxxxxxxxxxxxx>
> Signed-off-by: Caterina Shablia <caterina.shablia@xxxxxxxxxxxxx>

In v4 I also mentioned:

	I also think this feature deserves its own section in the global GPUVM
	documentation -- please add a corresponding paragraph.

	Also it seems that we need to update the documentation which shows all potential
	cases when calling __drm_gpuvm_sm_map() [1].

	[1] https://docs.kernel.org/gpu/drm-mm.html#split-and-merge

Why did this not happen?

> +static int validate_map_request(struct drm_gpuvm *gpuvm,
> +				const struct drm_gpuva_op_map *op)
> +{
> +	if (unlikely(!drm_gpuvm_range_valid(gpuvm, op->va.addr, op->va.range)))
> +		return -EINVAL;
> +
> +	if (op->flags & DRM_GPUVA_REPEAT) {
> +		u64 va_range = op->va.range;
> +
> +		/* For a repeated mapping, GEM range must be > 0
> +		 * and a multiple of the VA range.
> +		 */
> +		if (unlikely(!op->gem.repeat_range ||
> +			     va_range < op->gem.repeat_range ||
> +			     do_div(va_range, op->gem.repeat_range)))
> +			return -EINVAL;
> +	}
> +
> +	if (op->flags & DRM_GPUVA_INVALIDATED)
> +		return -EINVAL;

This seems unrelated to this patch.

> +
> +	return 0;
> +}
> +
>  static int
>  __drm_gpuvm_sm_map(struct drm_gpuvm *gpuvm,
>  		   const struct drm_gpuvm_ops *ops, void *priv,
> @@ -2429,7 +2475,8 @@ __drm_gpuvm_sm_map(struct drm_gpuvm *gpuvm,
>  	u64 req_end = req_addr + req_range;
>  	int ret;
>  
> -	if (unlikely(!drm_gpuvm_range_valid(gpuvm, req_addr, req_range)))
> +	ret = validate_map_request(gpuvm, &req->map);
> +	if (unlikely(ret))
>  		return -EINVAL;
>  
>  	drm_gpuvm_for_each_va_range_safe(va, next, gpuvm, req_addr, req_end) {
> @@ -2463,7 +2510,9 @@ __drm_gpuvm_sm_map(struct drm_gpuvm *gpuvm,
>  					.va.addr = req_end,
>  					.va.range = range - req_range,
>  					.gem.obj = obj,
> -					.gem.offset = offset + req_range,
> +					.gem.repeat_range = va->gem.repeat_range,
> +					.gem.offset = offset +
> +						(va->flags & DRM_GPUVA_REPEAT ? 0 : req_range),

This seems to be a repeating pattern, can we factor this into a helper?