Re: [Xen-devel] [PATCH v3 05/11] optee: add fast calls handling

[Julien Grall <julien.grall@xxxxxxx>]

Hi Volodymyr,

On 18/12/2018 21:11, Volodymyr Babchuk wrote:
> From: Volodymyr Babchuk <vlad.babchuk@xxxxxxxxx>
>
> Some fast SMCCC calls to OP-TEE should be handled in a special way.
> 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.
I haven't seen an answer to my question on the previous version. For reminder:

Would it make sense to still allow the hardware domain to access static SHM?

Cheers,

--
Julien Grall

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