[PATCH 6.18.y] accel/amdxdna: return early from a zero-length flush

[Sasha Levin <sashal@kernel.org>]

From: Taimuraz Kaitmazov <taimuraz@kaitmazov.com>

[ Upstream commit dc14753664240cedf669623b27ae9922b0618b25 ]

SYNC_BO does not constrain its size, so a request for zero bytes reaches
drm_clflush_virt_range(), which ends with an unconditional
clflushopt(end - 1). For an empty range that is the byte before the
mapping, and abo->mem.kva comes from vmap(), so the access lands in the
guard page below the vmalloc area and faults:

  BUG: unable to handle page fault for address: ffffd16fbbc70fff
  #PF: supervisor read access in kernel mode
  Oops: Oops: 0000 [#1] SMP NOPTI
  CPU: 7 UID: 1000 Comm: sync_bo_probe
  RIP: 0010:drm_clflush_virt_range+0x3c/0x70
  Call Trace:
   amdxdna_drm_sync_bo_ioctl+0x124/0x430 [amdxdna]
   drm_ioctl+0x301/0x4c0
   __x64_sys_ioctl+0x115/0x2f0
   do_syscall_64+0xa6/0x3d0

Any process that can open the render node can do this. Reproduced 3 of 3
times on a Strix Point NPU (1022:17f0), by calling SYNC_BO with size 0 on
an AMDXDNA_BO_SHARE object. The import arm takes the same request but
flushes the whole scatterlist, so it survives it.

Nothing needs flushing for an empty range, so answer before choosing a
path.

Fixes: e252e3f3488a ("accel/amdxdna: Revise device bo creation and free")
Cc: stable@vger.kernel.org
Signed-off-by: Taimuraz Kaitmazov <taimuraz@kaitmazov.com>
Reviewed-by: Lizhi Hou <lizhi.hou@amd.com>
Signed-off-by: Lizhi Hou <lizhi.hou@amd.com>
Link: https://patch.msgid.link/20260817230655.356785-1-taimuraz@kaitmazov.com
[ moved the guard into amdxdna_drm_sync_bo_ioctl() because amdxdna_flush_bo() is absent. ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/accel/amdxdna/amdxdna_gem.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/accel/amdxdna/amdxdna_gem.c b/drivers/accel/amdxdna/amdxdna_gem.c
index a719dc6aab339..ca747457cec79 100644
--- a/drivers/accel/amdxdna/amdxdna_gem.c
+++ b/drivers/accel/amdxdna/amdxdna_gem.c
@@ -949,6 +949,9 @@ int amdxdna_drm_sync_bo_ioctl(struct drm_device *dev,
 		goto put_obj;
 	}
 
+	if (!args->size)
+		goto unpin;
+
 	if (is_import_bo(abo))
 		drm_clflush_sg(abo->base.sgt);
 	else if (abo->mem.kva)
@@ -958,6 +961,7 @@ int amdxdna_drm_sync_bo_ioctl(struct drm_device *dev,
 	else
 		drm_WARN(&xdna->ddev, 1, "Can not get flush memory");
 
+unpin:
 	amdxdna_gem_unpin(abo);
 
 	XDNA_DBG(xdna, "Sync bo %d offset 0x%llx, size 0x%llx\n",
-- 
2.53.0