Re: [XEN PATCH v8 21/22] xen/arm: ffa: list current limitations

[Julien Grall <julien@xxxxxxx>]

Hi Jens,

On 13/04/2023 08:14, Jens Wiklander wrote:
> Adds a comments with a list of unsupported FF-A interfaces and
> limitations in the implemented FF-A interfaces.
>
> Signed-off-by: Jens Wiklander <jens.wiklander@xxxxxxxxxx>
> ---
>   xen/arch/arm/tee/ffa.c | 32 ++++++++++++++++++++++++++++++++
>   1 file changed, 32 insertions(+)
>
> diff --git a/xen/arch/arm/tee/ffa.c b/xen/arch/arm/tee/ffa.c
> index 0948cc636871..6424c222c885 100644
> --- a/xen/arch/arm/tee/ffa.c
> +++ b/xen/arch/arm/tee/ffa.c
> @@ -13,6 +13,38 @@
>    *                https://developer.arm.com/documentation/den0077/e
>    * TEEC-1.0C: TEE Client API Specification version 1.0c available at
>    *            
> https://globalplatform.org/specs-library/tee-client-api-specification/
> + *
> + * Notes on the the current implementstion.
> + *
> + * Unsupported FF-A interfaces:
> + * o FFA_MSG_POLL and FFA_MSG_SEND - deprecated in FF-A-1.1-REL0
> + * o FFA_MEM_RETRIEVE_* - Used when sharing memory from an SP to a VM
> + * o FFA_MEM_DONATE_* and FFA_MEM_LEND_* - Used when tranferring ownership
> + *   or access of a memory readion
> + * o FFA_MSG_SEND2 and FFA_MSG_WAIT - Used for indirect messaging
> + * o FFA_MSG_YIELD
> + * o FFA_INTERRUPT - Used to report preemption
> + * o FFA_RUN
> + *
> + * Limitations in the implemented FF-A interfaces:
> + * o FFA_RXTX_MAP_*:
> + *   - Maps at most 32 4k pages large RX and TX buffers
> + *   - RT/TX buffers must be normal RAM
Can you explain why this is a problem?

> + *   - Doesn't support forwarding this call on behalf of an endpoint
> + * o FFA_MEM_SHARE_*: only supports sharing
> + *   - from a VM to an SP
> + *   - with one borrower
> + *   - with the memory transaction descriptor in the RX/TX buffer
> + *   - normal memory
> + *   - at most 512 kB large memory regions
> + *   - at most 32 shared memory regions per guest
> + * o FFA_MSG_SEND_DIRECT_REQ:
> + *   - only supported from a VM to an SP
> + *
> + * There are some large locked sections with ffa_tx_buffer_lock and
> + * ffa_rx_buffer_lock. Especially the ffa_tx_buffer_lock spinlock used
> + * around share_shm() is a very large locked section which can let one VM
> + * affect another VM.
>    */
>   
>   #include <xen/bitops.h>
Cheers,

--
Julien Grall