[PATCH] drm/xe/dma_buf: stop relying on placement in unmap

[Matthew Auld <matthew.auld@intel.com>]

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;
 		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);
-- 
2.49.0