Re: [PATCH] drm/xe: Allow mixed mappings for userptr

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

Hi,

On Wed, 2025-09-17 at 11:28 -0700, Matthew Brost wrote:
> Compute kernels often issue memory copies immediately after
> completion.
> If the memory being copied is an SVM pointer that was faulted into
> the
> device and then bound via userptr, it is undesirable to move that
> memory. Worse, if userptr is mixed between system and device memory,
> the
> bind operation may be rejected.
> 
> Xe already has the necessary plumbing to support userptr with mixed
> mappings. This update modifies GPUSVM's get_pages to correctly locate
> pages in such mixed mapping scenarios.
> 
> Fixes: ("9e9787414882 drm/xe/userptr: replace xe_hmm with gpusvm")
> Signed-off-bt: Matthew Brost <matthew.brost@intel.com>

s/bt/by/

Perhaps we need to let the PAT index discussion land before we merge
this. If we support multiple placements we might need multiple PAT
indices...

Otherwise LGTM.

Thanks,
Thomas


> ---
>  drivers/gpu/drm/drm_gpusvm.c    | 6 ++++--
>  drivers/gpu/drm/xe/xe_userptr.c | 1 +
>  include/drm/drm_gpusvm.h        | 4 ++++
>  3 files changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_gpusvm.c
> b/drivers/gpu/drm/drm_gpusvm.c
> index eeeeb99cfdf6..64c0ea70eae3 100644
> --- a/drivers/gpu/drm/drm_gpusvm.c
> +++ b/drivers/gpu/drm/drm_gpusvm.c
> @@ -1361,7 +1361,8 @@ int drm_gpusvm_get_pages(struct drm_gpusvm
> *gpusvm,
>  		order = drm_gpusvm_hmm_pfn_to_order(pfns[i], i,
> npages);
>  		if (is_device_private_page(page) ||
>  		    is_device_coherent_page(page)) {
> -			if (zdd != page->zone_device_data && i > 0)
> {
> +			if (!ctx->allow_mixed &&
> +			    zdd != page->zone_device_data && i > 0)
> {
>  				err = -EOPNOTSUPP;
>  				goto err_unmap;
>  			}
> @@ -1397,7 +1398,8 @@ int drm_gpusvm_get_pages(struct drm_gpusvm
> *gpusvm,
>  		} else {
>  			dma_addr_t addr;
>  
> -			if (is_zone_device_page(page) || pagemap) {
> +			if (is_zone_device_page(page) ||
> +			    (pagemap && !ctx->allow_mixed)) {
>  				err = -EOPNOTSUPP;
>  				goto err_unmap;
>  			}
> diff --git a/drivers/gpu/drm/xe/xe_userptr.c
> b/drivers/gpu/drm/xe/xe_userptr.c
> index 91d09af71ced..c628f58c085c 100644
> --- a/drivers/gpu/drm/xe/xe_userptr.c
> +++ b/drivers/gpu/drm/xe/xe_userptr.c
> @@ -54,6 +54,7 @@ int xe_vma_userptr_pin_pages(struct xe_userptr_vma
> *uvma)
>  	struct xe_device *xe = vm->xe;
>  	struct drm_gpusvm_ctx ctx = {
>  		.read_only = xe_vma_read_only(vma),
> +		.allow_mixed = true,
>  	};
>  
>  	lockdep_assert_held(&vm->lock);
> diff --git a/include/drm/drm_gpusvm.h b/include/drm/drm_gpusvm.h
> index 5434048a2ca4..97d2f57914bb 100644
> --- a/include/drm/drm_gpusvm.h
> +++ b/include/drm/drm_gpusvm.h
> @@ -235,6 +235,9 @@ struct drm_gpusvm {
>   * @read_only: operating on read-only memory
>   * @devmem_possible: possible to use device memory
>   * @devmem_only: use only device memory
> + * @allow_mixed: Allow mixed mappings in get pages. Mixing between
> system and
> + *               single dpagemap is supported, mixing between
> multiple dpagemap
> + *               is unsupported.
>   *
>   * Context that is DRM GPUSVM is operating in (i.e. user arguments).
>   */
> @@ -245,6 +248,7 @@ struct drm_gpusvm_ctx {
>  	unsigned int read_only :1;
>  	unsigned int devmem_possible :1;
>  	unsigned int devmem_only :1;
> +	unsigned int allow_mixed :1;
>  };
>  
>  int drm_gpusvm_init(struct drm_gpusvm *gpusvm,