[PATCH v4 4/5] accel/amdxdna: refuse to flush an imported BO

SYNC_BO clflushes an imported BO's scatterlist. An importer may not do
that: the memory belongs to the exporter, and dma-buf gives the importer
no interface to ask for maintenance on it. Refuse the request instead.

is_import_bo() is (obj)->attach, which covers more than foreign buffers.
A userptr BO arrives through a ubuf, and on a carveout device every share
BO and the device heap arrive through a cbuf, so SYNC_BO answers
-EOPNOTSUPP for those too, including the AMDXDNA_BO_DEV path that flushes
through its heap.

Only the ubuf case gives up maintenance it was getting: on a 64 MiB
userptr BO a 4 KiB sync and a full sync both cost 659 us, this arm having
ignored the range. amdxdna_cbuf_map() fills in only the DMA address and
length, so drm_clflush_sg() already walks zero pages on carveout memory.
Userspace maintains these through the mapping it already holds, as XRT's
buffer::sync() does unless it is told to sync through the driver.

Suggested-by: Lizhi Hou <[email protected]>
Signed-off-by: Taimuraz Kaitmazov <[email protected]>
---
 drivers/accel/amdxdna/amdxdna_gem.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/accel/amdxdna/amdxdna_gem.c b/drivers/accel/amdxdna/amdxdna_gem.c
index 4f38f985c74e..a713a9982d34 100644
--- a/drivers/accel/amdxdna/amdxdna_gem.c
+++ b/drivers/accel/amdxdna/amdxdna_gem.c
@@ -1224,6 +1224,9 @@ static int amdxdna_flush_bo(struct amdxdna_gem_obj *abo, u64 offset, u64 size)
 {
 	u64 end;
 
+	if (is_import_bo(abo))
+		return -EOPNOTSUPP;
+
 	if (offset >= abo->mem.size)
 		return -EINVAL;
 
@@ -1234,9 +1237,7 @@ static int amdxdna_flush_bo(struct amdxdna_gem_obj *abo, u64 offset, u64 size)
 	if (!size)
 		return 0;
 
-	if (is_import_bo(abo))
-		drm_clflush_sg(abo->base.sgt);
-	else if (amdxdna_gem_vmap(abo))
+	if (amdxdna_gem_vmap(abo))
 		drm_clflush_virt_range(amdxdna_gem_vmap(abo) + offset, size);
 	else if (abo->base.pages)
 		drm_clflush_pages(abo->base.pages, abo->mem.size >> PAGE_SHIFT);
-- 
2.55.0