Re: [PATCH v3 18/33] drm/xe: Handle defrag moves in xe_bo_move()

[Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>]

On Fri, Jul 10, 2026 at 07:56:04PM -0700, Matthew Brost wrote:
>Teach xe_bo_move() to service a defrag move, where TTM reallocates a
>BO's backing at the device's beneficial order and hands the old, still
>populated tt to the move via the BO's defrag_old_tt.
>
>A defrag move always has existing contents to copy, so force
>move_lacks_source false and fall through the XE_PL_TT -> XE_PL_TT no-op
>shortcut so the copy path runs. The relocation is performed entirely on
>the GPU via xe_migrate_copy_defrag(), reading the old pages from the
>stashed tt's sg table and writing the freshly reallocated backing.
>
>Both copy passes run in order on the same migrate queue and are captured
>by the returned fence, so the teardown is pipelined via
>ttm_bo_move_accel_cleanup(): the old tt is handed to a ghost object and
>only unpopulated and freed once the fence signals, so the move need not
>block. The VF CCS attach/detach handling is extended to treat a defrag
>move (ctx->defrag) like the XE_PL_SYSTEM <-> XE_PL_TT transitions it
>mirrors.
>
>Cc: Carlos Santa <carlos.santa@intel.com>
>Cc: Ryan Neph <ryanneph@google.com>
>Cc: Christian Koenig <christian.koenig@amd.com>
>Cc: Huang Rui <ray.huang@amd.com>
>Cc: Matthew Auld <matthew.auld@intel.com>
>Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
>Cc: Maxime Ripard <mripard@kernel.org>
>Cc: Thomas Zimmermann <tzimmermann@suse.de>
>Cc: David Airlie <airlied@gmail.com>
>Cc: Simona Vetter <simona@ffwll.ch>
>Cc: dri-devel@lists.freedesktop.org
>Cc: linux-kernel@vger.kernel.org
>Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
>Assisted-by: GitHub_Copilot:claude-opus-4.8
>Signed-off-by: Matthew Brost <matthew.brost@intel.com>
>---
> drivers/gpu/drm/xe/xe_bo.c | 24 ++++++++++++++++++++----
> 1 file changed, 20 insertions(+), 4 deletions(-)
>
>diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c
>index 02395968d613..bdcc9bed5d36 100644
>--- a/drivers/gpu/drm/xe/xe_bo.c
>+++ b/drivers/gpu/drm/xe/xe_bo.c
>@@ -1170,6 +1170,13 @@ static int xe_bo_move(struct ttm_buffer_object *ttm_bo, bool evict,
> 	move_lacks_source = !old_mem || (handle_system_ccs ? (!bo->ccs_cleared) :
> 					 (!mem_type_is_vram(old_mem_type) && !tt_has_data));
>
>+	/*
>+	 * A defrag move always copies the existing contents from the stashed
>+	 * old tt into the freshly (re)allocated backing.
>+	 */
>+	if (ttm_bo->defrag_old_tt)
>+		move_lacks_source = false;
>+
> 	needs_clear = (ttm && ttm->page_flags & TTM_TT_FLAG_ZERO_ALLOC) ||
> 		(!ttm && ttm_bo->type == ttm_bo_type_device);
>
>@@ -1206,9 +1213,12 @@ static int xe_bo_move(struct ttm_buffer_object *ttm_bo, bool evict,
> 	/*
> 	 * Failed multi-hop where the old_mem is still marked as
> 	 * TTM_PL_FLAG_TEMPORARY, should just be a dummy move.
>+	 *
>+	 * For a defrag move the old and new tt differ, so fallthrough to the
>+	 * copy path instead of treating it as a no-op.
> 	 */
> 	if (old_mem_type == XE_PL_TT &&
>-	    new_mem->mem_type == XE_PL_TT) {
>+	    new_mem->mem_type == XE_PL_TT && !ttm_bo->defrag_old_tt) {
> 		ttm_bo_move_null(ttm_bo, new_mem);
> 		goto out;
> 	}
>@@ -1279,6 +1289,12 @@ static int xe_bo_move(struct ttm_buffer_object *ttm_bo, bool evict,
> 			flags |= XE_MIGRATE_CLEAR_FLAG_CCS_DATA;
>
> 		fence = xe_migrate_clear(migrate, bo, new_mem, flags);
>+	} else if (ttm_bo->defrag_old_tt) {
>+		struct xe_ttm_tt *old_xe_tt =
>+			container_of(ttm_bo->defrag_old_tt, struct xe_ttm_tt, ttm);
>+
>+		fence = xe_migrate_copy_defrag(migrate, bo, old_mem, new_mem,
>+					       old_xe_tt->sg, handle_system_ccs);
> 	} else {
> 		fence = xe_migrate_copy(migrate, bo, bo, old_mem, new_mem,
> 					handle_system_ccs);
>@@ -1315,13 +1331,13 @@ static int xe_bo_move(struct ttm_buffer_object *ttm_bo, bool evict,
> 	 * BBs from BO as it is no longer needed.
> 	 */
> 	if (IS_VF_CCS_READY(xe) && old_mem_type == XE_PL_TT &&
>-	    new_mem->mem_type == XE_PL_SYSTEM)
>+	    (new_mem->mem_type == XE_PL_SYSTEM || ctx->defrag))
> 		xe_sriov_vf_ccs_detach_bo(bo);
>
> 	if (IS_VF_CCS_READY(xe) &&
> 	    ((move_lacks_source && new_mem->mem_type == XE_PL_TT) ||
>-	     (old_mem_type == XE_PL_SYSTEM && new_mem->mem_type == XE_PL_TT)) &&
>-	    handle_system_ccs)
>+	     ((old_mem_type == XE_PL_SYSTEM || ctx->defrag) &&
>+	      new_mem->mem_type == XE_PL_TT)) && handle_system_ccs)
> 		ret = xe_sriov_vf_ccs_attach_bo(bo);

Assisted-by: LLM

Looks like code has changed in drm-tip and sriov_vf_ccs_attach/detach changes here
needs to be rebased.

There are also some sashiko reported bugs around this sriov_vf_ccs_attach_bo which
looks legitimate (like move() function returning earlier in error case while move
is in progress).

Niranjana

>
> out:
>-- 
>2.34.1
>