From: Harkirat Gill Date: Mon, 27 Jul 2026 18:37:56 +0000 (-0400) Subject: drm/amdgpu: cap GTT size to physical RAM on APUs X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=5e70f6804b4d6256058c360b10e044ee04ea4a4e;p=thirdparty%2Flinux.git drm/amdgpu: cap GTT size to physical RAM on APUs On APUs, the GTT pool is backed by system RAM, but its size is not bound to the non-carveout memory that actually backs it. A user can end up with GTT + VRAM exceeding total physical memory through the following sequence: - Have a large non-carveout memory space (~128GB) and accordingly set a large GTT (~100GB) via the ttm module parameter. - Lower the non-carveout memory space in BIOS by increasing the UMA Frame Buffer Size (VRAM) to 64GB. - The previously set GTT value (~100GB) persists, even though the new non-carveout space (64GB) can no longer back it. This leads to a case where kernel reports GTT (100GB) + VRAM (64GB) despite the sum being greater than total physical memory (128GB). Cap the GTT size to totalram_pages() on APUs. totalram_pages() already excludes the VRAM carveout, so the resulting GTT can never exceed the system RAM that actually backs it. Signed-off-by: Harkirat Gill Reviewed-by: David Francis Assisted-by: Claude:claude-opus-4 Signed-off-by: Alex Deucher (cherry picked from commit 5dafdd649280c7dc6c22c8f877da3f54fcc441e1) Cc: stable@vger.kernel.org --- diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c index eb8bbfc7e6d9..5fc91f45db5b 100644 --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c @@ -2173,6 +2173,18 @@ int amdgpu_ttm_init(struct amdgpu_device *adev) gtt_size = configured_size; } + /* Cap GTT so that it does not exceed total physical RAM. */ + if (adev->flags & AMD_IS_APU) { + u64 phys_ram = (u64)totalram_pages() << PAGE_SHIFT; + + if (gtt_size > phys_ram) { + gtt_size = phys_ram; + dev_info(adev->dev, + "Capping GTT to %uM to not exceed available system memory\n", + (unsigned int)(gtt_size / (1024 * 1024))); + } + } + /* Initialize GTT memory pool */ r = amdgpu_gtt_mgr_init(adev, gtt_size); if (r) {