From: Boris Brezillon Date: Fri, 2 Jan 2026 20:37:23 +0000 (-0800) Subject: drm/panthor: Flush shmem writes before mapping buffers CPU-uncached X-Git-Tag: v6.12.64~43 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=8355eea2a2e9c323021dfdcb95d7767d382123c4;p=thirdparty%2Fkernel%2Fstable.git 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 Reviewed-by: Steven Price Reviewed-by: Liviu Dudau Signed-off-by: Steven Price 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 Signed-off-by: Greg Kroah-Hartman --- diff --git a/drivers/gpu/drm/panthor/panthor_gem.c b/drivers/gpu/drm/panthor/panthor_gem.c index 0438b80a6434b..09b318fb8e7cd 100644 --- a/drivers/gpu/drm/panthor/panthor_gem.c +++ b/drivers/gpu/drm/panthor/panthor_gem.c @@ -214,6 +214,23 @@ panthor_gem_create_with_handle(struct drm_file *file, bo->base.base.resv = bo->exclusive_vm_root_gem->resv; } + /* If this is a write-combine mapping, we query the sgt to force a CPU + * cache flush (dma_map_sgtable() is called when the sgt is created). + * This ensures the zero-ing is visible to any uncached mapping created + * by vmap/mmap. + * FIXME: Ideally this should be done when pages are allocated, not at + * BO creation time. + */ + if (shmem->map_wc) { + struct sg_table *sgt; + + sgt = drm_gem_shmem_get_pages_sgt(shmem); + if (IS_ERR(sgt)) { + ret = PTR_ERR(sgt); + goto out_put_gem; + } + } + /* * Allocate an id of idr table where the obj is registered * and handle has the id what user can see. @@ -222,6 +239,7 @@ panthor_gem_create_with_handle(struct drm_file *file, if (!ret) *size = bo->base.base.size; +out_put_gem: /* drop reference from allocate - handle holds it now. */ drm_gem_object_put(&shmem->base);