Re: [PATCH 2/2] drm/xe/vm: make PREFETCH to TT sticky

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

On Mon, 2026-09-28 at 17:48 +0100, Matthew Auld wrote:
> When userspace explicitly requests DRM_XE_VM_BIND_OP_PREFETCH to
> system
> memory (XE_PL_TT), xe_bo_migrate() moves the buffer object to TT.
> However, because XE_PL_TT is marked with TTM_PL_FLAG_FALLBACK in the
> buffer's default placement (introduced in commit 5c87fee3c96c
> ("drm/xe:
> Attempt to bring bos back to VRAM after eviction")), any subsequent
> validation during exec immediately migrates the buffer back to VRAM,
> completely undoing the userspace prefetch request.
> 
> Use xe_bo_migrate_tt_sticky() when prefetching to XE_PL_TT so that
> the
> buffer remains resident in system memory across subsequent
> validations.
> 
> Assisted-by: LLM
> Reported-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> Fixes: 5c87fee3c96c ("drm/xe: Attempt to bring bos back to VRAM after
> eviction")
> Signed-off-by: Matthew Auld <matthew.auld@intel.com>
> Cc: Matthew Brost <matthew.brost@intel.com>
> Cc: <stable@vger.kernel.org> # v6.12+

I think we need somewhere to clear this stickiness. Perhaps if
xe_bo_migrate() is called with another destination than the sticky one,
we'd clear it?

Thanks,
Thomas




> ---
>  drivers/gpu/drm/xe/xe_vm.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
> index 425c678f4480..2068e0cf50ff 100644
> --- a/drivers/gpu/drm/xe/xe_vm.c
> +++ b/drivers/gpu/drm/xe/xe_vm.c
> @@ -3406,7 +3406,10 @@ static int op_lock_and_prep(struct drm_exec
> *exec, struct xe_vm *vm,
>  				mem_type =
> region_to_mem_type[region];
>  			}
>  
> -			err = xe_bo_migrate(bo, mem_type, NULL,
> exec);
> +			if (mem_type == XE_PL_TT)
> +				err = xe_bo_migrate_tt_sticky(bo,
> NULL, exec);
> +			else
> +				err = xe_bo_migrate(bo, mem_type,
> NULL, exec);
>  		}
>  		break;
>  	}