Re: [PATCH v4 5/5] xen/arm: ffa: Enable VM to VM without firmware

[Julien Grall <julien@xxxxxxx>]

On 26/03/2025 23:41, Julien Grall wrote:
> Hi Bertrand,
>
> On 24/03/2025 13:53, Bertrand Marquis wrote:
> > When VM to VM support is activated and there is no suitable FF-A support
> > in the firmware, enable FF-A support for VMs to allow using it for VM to
> > VM communications.
> tee/ and the callbacks associated are meant to be used for mediatiors. 
> My current interpretation ist this is only meant to interpose between a 
> guest and physical resources. Here you are extending the meaning to 
> "virtual TEE". I am sort of ok with that but ...
> > If there is OP-TEE running in the secure world and using the non FF-A
> > communication system, having CONFIG_FFA_VM_TO_VM could be non functional
> > (if optee is probed first) or OP-TEE could be non functional (if FF-A is
> > probed first) so it is not recommended to activate the configuration
> > option for such systems.
> ... this part is concerning me. You should be able to build with 
> CONFIG_FFA_VM_TO_VM and still boot when OP-TEE is present on the system. 
> This is not too critical now as this is tech preview but this is 
> definitely a blocker for making FFA supported. Can this be mentioned at 
> the top of the ffa.c file (which already contains existing blocker)?
Just to clarify, I meant without having the OP-TEE folks to force the 
TEE on the command line because this is a bit of a hack...
Cheers,

--
Julien Grall