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;@@ -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);