Re: [Xen-devel] [PATCH v5 04/10] xen/arm: optee: add fast calls handling

[Julien Grall <julien.grall@xxxxxxx>]

Hi Volodymyr,

On 21/05/2019 22:25, Volodymyr Babchuk wrote:
> This patch adds handling for the fast SMCs. As name suggests, those
> calls can't be preempted and are used for auxiliary tasks such as
> information retrieval. Most handlers are quite trivial, with exception
> for capabilities information.
>
> Capabilities exchange should be filtered out, so only caps
> known to mediator are used. Also mediator disables static SHM
> memory capability, because it can't share OP-TEE memory with a domain.
> Only domain can share memory with OP-TEE, so it ensures that OP-TEE
> supports dynamic SHM.
>
> Basically, static SHM is a reserved memory region which is always
> mapped into OP-TEE address space. It belongs to OP-TEE. Normally,
> NW is allowed to access there, so it can communicate with OP-TEE.
>
> On other hand, dynamic SHM is NW's own memory, which it can share
> with OP-TEE. OP-TEE maps this memory dynamically, when it wants to
> access it.
>
> Because mediator can't share one static SHM region with all guests, it
> just disables it for all of them. It is possible to make exception for
> Dom0, but it requires separate handling for buffers allocated from
> that region. Thus, it is not implemented yet.
>
> Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>
Acked-by: Julien Gral <julien.grall@xxxxxxx>

Cheers,

--
Julien Grall

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