drm/panthor: Flush shmem writes before mapping buffers CPU-uncached

drm/panthor: Flush shmem writes before mapping buffers CPU-uncached

[ Upstream commit 576c930e5e7dcb937648490611a83f1bf0171048 ]

The shmem layer zeroes out the new pages using cached mappings, and if
we don't CPU-flush we might leave dirty cachelines behind, leading to
potential data leaks and/or asynchronous buffer corruption when dirty
cachelines are evicted.

Fixes: 8a1cc07578bf ("drm/panthor: Add GEM logical block")
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>
Signed-off-by: Steven Price <steven.price@arm.com>
Link: https://patch.msgid.link/20251107171214.1186299-1-boris.brezillon@collabora.com
[Harshit: Resolve conflicts due to missing commit: fe69a3918084
("drm/panthor: Fix UAF in panthor_gem_create_with_handle() debugfs
code") in 6.12.y]
Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>