On Thu, 30 Jan 2025 17:15:24 +0100
Simona Vetter [off-list ref] wrote:

On Thu, Jan 30, 2025 at 01:08:56PM +0000, Florent Tomasin wrote:

quoted

Hi,

This is a patch series covering the support for protected mode execution in
Mali Panthor CSF kernel driver.

The Mali CSF GPUs come with the support for protected mode execution at the
HW level. This feature requires two main changes in the kernel driver:

1) Configure the GPU with a protected buffer. The system must provide a DMA
   heap from which the driver can allocate a protected buffer.
   It can be a carved-out memory or dynamically allocated protected memory region.
   Some system includes a trusted FW which is in charge of the protected memory.
   Since this problem is integration specific, the Mali Panthor CSF kernel
   driver must import the protected memory from a device specific exporter.

2) Handle enter and exit of the GPU HW from normal to protected mode of execution.
   FW sends a request for protected mode entry to the kernel driver.
   The acknowledgment of that request is a scheduling decision. Effectively,
   protected mode execution should not overrule normal mode of execution.
   A fair distribution of execution time will guaranty the overall performance
   of the device, including the UI (usually executing in normal mode),
   will not regress when a protected mode job is submitted by an application.


Background
----------

Current Mali Panthor CSF driver does not allow a user space application to
execute protected jobs on the GPU. This use case is quite common on end-user-device.
A user may want to watch a video or render content that is under a "Digital Right
Management" protection, or launch an application with user private data.

1) User-space:

   In order for an application to execute protected jobs on a Mali CSF GPU the
   user space application must submit jobs to the GPU within a "protected regions"
   (range of commands to execute in protected mode).

   Find here an example of a command buffer that contains protected commands:

          <--- Normal mode ---><--- Protected mode ---><--- Normal mode --->
   +-------------------------------------------------------------------------+
   | ... | CMD_0 | ... | CMD_N | PROT_REGION | CMD_N+1 | ... | CMD_N+M | ... |
   +-------------------------------------------------------------------------+

   The PROT_REGION command acts as a barrier to notify the HW of upcoming
   protected jobs. It also defines the number of commands to execute in protected
   mode.

   The Mesa definition of the opcode can be found here:

     https://gitlab.freedesktop.org/mesa/mesa/-/blob/main/src/panfrost/lib/genxml/v10.xml?ref_type=heads#L763  

Is there also something around that implements egl_ext_protected_context
or similar in mesa?

I'll be looking at a mesa implementation for EGL_EXT_protected_content
in the coming weeks. I'll probably get back to reviewing the panthor
implementation when I have something working in mesa.

I think that's the minimal bar all the protected gpu
workload kernel support patches cleared thus far, since usually getting
the actual video code stuff published seems to be impossible.