From 106b4a2a78b2a2f14885604891957b84bba502db Mon Sep 17 00:00:00 2001 From: Adrian Betschart Date: Fri, 11 Sep 2026 17:13:14 +0200 Subject: drm/amd/display: Try RGB before YCbCr 4:4:4 in stream validation amdgpu_dm_create_validate_stream_for_sink() walks encoding_order[] and uses the first encoding that validates. YCbCr 4:4:4 is listed before RGB, so an HDMI sink that advertises 4:4:4 gets YCbCr 4:4:4 whenever the "color format" property is left at AUTO, even though RGB fits the same link. That contradicts the documented AUTO behaviour for HDMI in enum drm_connector_color_format (RGB, falling back to YCbCr 4:2:0 only when the bandwidth is not available or the mode is 4:2:0-only), which the amdgpu implementation of the property also describes. It also leaves the "Broadcast RGB" property without effect on such sinks, since the quantization range it selects only applies to RGB output. Try RGB first. The mask still holds every encoding the sink supports, so a mode that cannot carry RGB falls back exactly as before. For reference, v7.2 picked RGB here unless YCbCr 4:4:4 was forced through debugfs, while earlier kernels picked YCbCr 4:4:4 for any HDMI sink that advertised it. Fixes: 0b0ff65d3ca1 ("drm/amd/display: Refactor stream validation") Suggested-by: Adolfo Rodrigues Assisted-by: Claude Code:claude-fable-5-1 Signed-off-by: Adrian Betschart Reviewed-by: Fangzhi Zuo Tested-by: Adolfo Rodrigues Tested-by: Daniel Wheeler Signed-off-by: Alex Deucher (cherry picked from commit 7de432bc753133764dc40d37f9388da56de251e7) --- .../admin-guide/namespaces/compatibility-list.rst | 43 ++++++++++++++++++++++ Documentation/admin-guide/namespaces/index.rst | 11 ++++++ .../admin-guide/namespaces/resource-control.rst | 18 +++++++++ 3 files changed, 72 insertions(+) create mode 100644 Documentation/admin-guide/namespaces/compatibility-list.rst create mode 100644 Documentation/admin-guide/namespaces/index.rst create mode 100644 Documentation/admin-guide/namespaces/resource-control.rst (limited to 'Documentation/admin-guide/namespaces') diff --git a/Documentation/admin-guide/namespaces/compatibility-list.rst b/Documentation/admin-guide/namespaces/compatibility-list.rst new file mode 100644 index 000000000..318800b2a --- /dev/null +++ b/Documentation/admin-guide/namespaces/compatibility-list.rst @@ -0,0 +1,43 @@ +============================= +Namespaces compatibility list +============================= + +This document contains the information about the problems user +may have when creating tasks living in different namespaces. + +Here's the summary. This matrix shows the known problems, that +occur when tasks share some namespace (the columns) while living +in different other namespaces (the rows): + +==== === === === === ==== === +- UTS IPC VFS PID User Net +==== === === === === ==== === +UTS X +IPC X 1 +VFS X +PID 1 1 X +User 2 2 X +Net X +==== === === === === ==== === + +1. Both the IPC and the PID namespaces provide IDs to address + object inside the kernel. E.g. semaphore with IPCID or + process group with pid. + + In both cases, tasks shouldn't try exposing this ID to some + other task living in a different namespace via a shared filesystem + or IPC shmem/message. The fact is that this ID is only valid + within the namespace it was obtained in and may refer to some + other object in another namespace. + +2. Intentionally, two equal user IDs in different user namespaces + should not be equal from the VFS point of view. In other + words, user 10 in one user namespace shouldn't have the same + access permissions to files, belonging to user 10 in another + namespace. + + The same is true for the IPC namespaces being shared - two users + from different user namespaces should not access the same IPC objects + even having equal UIDs. + + But currently this is not so. diff --git a/Documentation/admin-guide/namespaces/index.rst b/Documentation/admin-guide/namespaces/index.rst new file mode 100644 index 000000000..384f2e0f3 --- /dev/null +++ b/Documentation/admin-guide/namespaces/index.rst @@ -0,0 +1,11 @@ +.. SPDX-License-Identifier: GPL-2.0 + +========== +Namespaces +========== + +.. toctree:: + :maxdepth: 1 + + compatibility-list + resource-control diff --git a/Documentation/admin-guide/namespaces/resource-control.rst b/Documentation/admin-guide/namespaces/resource-control.rst new file mode 100644 index 000000000..553a44803 --- /dev/null +++ b/Documentation/admin-guide/namespaces/resource-control.rst @@ -0,0 +1,18 @@ +==================================== +User namespaces and resource control +==================================== + +The kernel contains many kinds of objects that either don't have +individual limits or that have limits which are ineffective when +a set of processes is allowed to switch their UID. On a system +where the admins don't trust their users or their users' programs, +user namespaces expose the system to potential misuse of resources. + +In order to mitigate this, we recommend that admins enable memory +control groups on any system that enables user namespaces. +Furthermore, we recommend that admins configure the memory control +groups to limit the maximum memory usable by any untrusted user. + +Memory control groups can be configured by installing the libcgroup +package present on most distros editing /etc/cgrules.conf, +/etc/cgconfig.conf and setting up libpam-cgroup. -- cgit v1.3.1