Re: [PATCH 2/2] drm/pagemap: Disable device-to-device migration

[Francois Dugast <francois.dugast@intel.com>]

On Wed, Jan 07, 2026 at 10:27:16AM -0800, Matthew Brost wrote:
> Device-to-device migration is causing xe_exec_system_allocator --r
> *race*no* to intermittently fail with engine resets and a kernel hang on
> a page lock. This should work but is clearly buggy somewhere. Disable
> device-to-device migration in the interim until the issue can be
> root-caused.
> 
> The only downside of disabling device-to-device migration is that memory
> will bounce through system memory during migration. However, this path
> should be rare, as it only occurs when madvise attributes are changed or
> atomics are used.
> 
> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> Fixes: ec265e1f1cfc ("drm/pagemap: Support source migration over interconnect")
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> ---
>  drivers/gpu/drm/drm_pagemap.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_pagemap.c b/drivers/gpu/drm/drm_pagemap.c
> index aa43a8475100..03ee39a761a4 100644
> --- a/drivers/gpu/drm/drm_pagemap.c
> +++ b/drivers/gpu/drm/drm_pagemap.c
> @@ -480,8 +480,18 @@ int drm_pagemap_migrate_to_devmem(struct drm_pagemap_devmem *devmem_allocation,
>  		.start		= start,
>  		.end		= end,
>  		.pgmap_owner	= pagemap->owner,
> -		.flags		= MIGRATE_VMA_SELECT_SYSTEM | MIGRATE_VMA_SELECT_DEVICE_COHERENT |
> -		MIGRATE_VMA_SELECT_DEVICE_PRIVATE,
> +		/*
> +		 * FIXME: MIGRATE_VMA_SELECT_DEVICE_PRIVATE intermittently
> +		 * causes 'xe_exec_system_allocator --r *race*no*' to trigger aa

s/aa/an/

Reviewed-by: Francois Dugast <francois.dugast@intel.com>

> +		 * engine reset and a hard hang due to getting stuck on a folio
> +		 * lock. This should work and needs to be root-caused. The only
> +		 * downside of not selecting MIGRATE_VMA_SELECT_DEVICE_PRIVATE
> +		 * is that device-to-device migrations won’t work; instead,
> +		 * memory will bounce through system memory. This path should be
> +		 * rare and only occur when the madvise attributes of memory are
> +		 * changed or atomics are being used.
> +		 */
> +		.flags		= MIGRATE_VMA_SELECT_SYSTEM | MIGRATE_VMA_SELECT_DEVICE_COHERENT,
>  	};
>  	unsigned long i, npages = npages_in_range(start, end);
>  	unsigned long own_pages = 0, migrated_pages = 0;
> -- 
> 2.34.1
>