On Thu, Apr 03, 2025 at 03:56:38PM +0100, Matthew Auld wrote:

On 03/04/2025 15:07, Matthew Auld wrote:

...

The is_vram() is checking the current placement, however if we consider exported VRAM with dynamic dma-buf, it looks possible for the xe driver to async evict the memory, notifying the importer, however importer does not have to call unmap_attachment() immediately, but rather just as "soon as possible", like when the dma-resv idles. Following from this we would then pipeline the move, attaching the fence to the manager, and then update the current placement. But when the unmap_attachment() runs at some later point we might see that is_vram() is now false, and take the complete wrong path when dma-unmapping the sg, leading to explosions.

To fix this rather make a note in the attachment if the sg was originally mapping vram or tt pages.

Link: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/4563 Fixes: dd08ebf6c352 ("drm/xe: Introduce a new DRM driver for Intel GPUs") Signed-off-by: Matthew Auld matthew.auld@intel.com Cc: Thomas Hellström thomas.hellstrom@linux.intel.com Cc: Matthew Brost matthew.brost@intel.com Cc: stable@vger.kernel.org # v6.8+

---

drivers/gpu/drm/xe/xe_dma_buf.c | 23 ++++++++++++++++++++--- 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/xe/xe_dma_buf.c b/drivers/gpu/drm/xe/xe_dma_buf.c index f67803e15a0e..b71058e26820 100644 --- a/drivers/gpu/drm/xe/xe_dma_buf.c +++ b/drivers/gpu/drm/xe/xe_dma_buf.c @@ -22,6 +22,22 @@ MODULE_IMPORT_NS("DMA_BUF"); +/**

• • struct xe_sg_info - Track the exported sg info
• */

+struct xe_sg_info {

• /** @is_vram: True if this sg is mapping VRAM. */
• bool is_vram;

+};

+static struct xe_sg_info tt_sg_info = {

• .is_vram = false,

+};

+static struct xe_sg_info vram_sg_info = {

• .is_vram = true,

+};

• static int xe_dma_buf_attach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach) {

@@ -118,6 +134,7 @@ static struct sg_table *xe_dma_buf_map(struct dma_buf_attachment *attach, if (dma_map_sgtable(attach->dev, sgt, dir, DMA_ATTR_SKIP_CPU_SYNC)) goto error_free;

• attach->priv = &tt_sg_info;
  

  break; case XE_PL_VRAM0:

@@ -128,6 +145,7 @@ static struct sg_table *xe_dma_buf_map(struct dma_buf_attachment *attach, dir, &sgt); if (r) return ERR_PTR(r);

• attach->priv = &vram_sg_info;
  

Maybe we need to subclass the sg itself? It looks possible to call map again, before the unmap, and you might get different memory if you had mixed placement bo...

I think that would be a better idea but drm_prime_pages_to_sg allocates the table so I think we'd a bit DRM rework to decouple the allocation from the implementation. Likewise xe_ttm_vram_mgr_alloc_sgt for too.

Matt

...

break;

default: return ERR_PTR(-EINVAL); @@ -145,10 +163,9 @@ static void xe_dma_buf_unmap(struct dma_buf_attachment *attach, struct sg_table *sgt, enum dma_data_direction dir) {

• struct dma_buf *dma_buf = attach->dmabuf;
• struct xe_bo *bo = gem_to_xe_bo(dma_buf->priv);

• struct xe_sg_info *sg_info = attach->priv;

• if (!xe_bo_is_vram(bo)) {

• if (!sg_info->is_vram) { dma_unmap_sgtable(attach->dev, sgt, dir, 0); sg_free_table(sgt); kfree(sgt);