Re: [PATCH v2 17/17] drm/xe/svm: Document how xe keeps drm_pagemap references

[Matthew Brost <matthew.brost@intel.com>]

On Tue, Nov 11, 2025 at 05:44:07PM +0100, Thomas Hellström wrote:
> As an aid to understanding the lifetime of the drm_pagemaps used
> by the xe driver, document how the xe driver keeps the
> drm_pagemap references.
> 
> Suggested-by: Matthew Brost <matthew.brost@intel.com>
> Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> ---
>  drivers/gpu/drm/xe/xe_svm.c | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/drivers/gpu/drm/xe/xe_svm.c b/drivers/gpu/drm/xe/xe_svm.c
> index 56bb3896b89a..c1d6eb2f97d1 100644
> --- a/drivers/gpu/drm/xe/xe_svm.c
> +++ b/drivers/gpu/drm/xe/xe_svm.c
> @@ -28,6 +28,28 @@
>  #define XE_PEER_PAGEMAP ((void *)0ul)
>  #define XE_PEER_VM ((void *)1ul)
>  
> +/**
> + * DOC: drm_pagemap reference-counting in xe:
> + *
> + * In addition to the drm_pagemap internal reference counting by
> + * its zone device data, the xe driver holds the following
> + * long-time references:
> + *
> + * - struct xe_pagemap:
> + *      The xe_pagemap struct derives from struct drm_pagemap and
> + *      uses its reference count.
> + * - SVM-enabled VMs:
> + *      SVM-enabled VMs look up and keeps a reference to all
> + *      xe_pagemaps on the same device.

Nit: I think the formatting looks slighly off with some too early line wraps.

Aside from the nit, LGTM:
Reviewed-by: Matthew Brost <matthew.brost@intel.com>

> + * - VMAs:
> + *      vmas keep a reference on the drm_pagemap indicated by a gpu_madvise()
> + *      call.
> + *
> + * In addition, all drm_pagemap or xe_pagemap pointers where lifetime cannot
> + * be guaranteed by a vma reference under the vm lock should keep a reference.
> + * That includes the range->pages.dpagemap pointer.
> + */
> +
>  static int xe_svm_get_pagemaps(struct xe_vm *vm);
>  
>  void *xe_svm_private_page_owner(struct xe_vm *vm, bool force_smem)
> -- 
> 2.51.1
>