Re: [PATCH 2/2] drm/xe: Allow mixed mappings for userptr

[Matthew Auld <matthew.auld@intel.com>]

On 08/10/2025 12:10, Thomas Hellström wrote:
> From: Matthew Brost <matthew.brost@intel.com>
> 
> 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.
> 
> v2:
> - Rebase (Thomas Hellström)
> 
> Fixes: ("9e9787414882 drm/xe/userptr: replace xe_hmm with gpusvm")
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com> #v1

Reviewed-by: Matthew Auld <matthew.auld@intel.com>

> ---
>   drivers/gpu/drm/drm_gpusvm.c    | 6 ++++--
>   drivers/gpu/drm/xe/xe_userptr.c | 4 +++-
>   include/drm/drm_gpusvm.h        | 4 ++++
>   3 files changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_gpusvm.c b/drivers/gpu/drm/drm_gpusvm.c
> index cb906765897e..73e550c8ff8c 100644
> --- a/drivers/gpu/drm/drm_gpusvm.c
> +++ b/drivers/gpu/drm/drm_gpusvm.c
> @@ -1363,7 +1363,8 @@ 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;
>   			}
> @@ -1399,7 +1400,8 @@ 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 f16e92cd8090..0d9130b1958a 100644
> --- a/drivers/gpu/drm/xe/xe_userptr.c
> +++ b/drivers/gpu/drm/xe/xe_userptr.c
> @@ -3,6 +3,7 @@
>    * Copyright © 2025 Intel Corporation
>    */
>   
> +#include "xe_svm.h"
>   #include "xe_userptr.h"
>   
>   #include <linux/mm.h>
> @@ -54,7 +55,8 @@ 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),
> -		.device_private_page_owner = NULL,
> +		.device_private_page_owner = xe_svm_devm_owner(xe),
> +		.allow_mixed = true,
>   	};
>   
>   	lockdep_assert_held(&vm->lock);
> diff --git a/include/drm/drm_gpusvm.h b/include/drm/drm_gpusvm.h
> index b92faa9a26b2..632e100e6efb 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).
>    */
> @@ -246,6 +249,7 @@ 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,