Re: [Xen-devel] [ARM] SMC (and HVC) handling in hypervisor

[Volodymyr Babchuk <vlad.babchuk@xxxxxxxxx>]

Hi, Julien

On 28 February 2017 at 15:51, Julien Grall <julien.grall@xxxxxxx> wrote:

>> This e-mail is sort of follow-up to the two threads: [1] (my thread
>> about TEE interaction) and [2] (Edgar's thread regarding handling SMC
>> calls in platform_hvc). I want to discuss more broad topic there.
>>
>> Obviously, there are growing number of SMC users and current state of
>> SMC handling in Xen satisfies nobody. My team wants to handle SMCs in
>> secure way, Xilinx wants to forward some calls directly to Secure
>> Monitor, while allowing to handle other in userspace, etc.
>>
>> My proposition is to gather all requirements to SMC (and HVC) handling
>> in one place (e.g. in this mail thread). After we' will have clear
>> picture of what we want, we will be able to develop some solution,
>> that will satisfy us all. At least, I hope so :)
>>
>> Also I want to remind, that there are ARM document called "SMC Calling
>> Convention" [3]. According to it, any aarch64 hypervisor "must
>> implement the Standard Secure and Hypervisor Service calls". At this
>> moment XEN does not conform to this.
>>
>> So, lets get started with the requirements:
>> 0. There are no much difference between SMC and HVC handling (at least
>> according to SMCCC).
>> 1. Hypervisor should at least provide own UUID and version while
>> called by SMC/HVC
>
>
> Do we need to reserve the UUID for Xen?
Yes, I think so. But I don't know the procedure. Should be that UUID
registered somewhere?
>
>> 2. Hypervisor should forward some calls from dom0 directly to Secure
>> Monitor (Xilinx use case)
>> 3. Hypervisor should virtualize PSCI calls, CPU service calls, ARM
>> architecture service calls, etc.
>> 4. Hypervisor should handle TEE calls in a secure way (e.g. no
>> untrusted handlers in Dom0 userspace).
>> 5. Hypervisor should support multiple TEEs (at least at compilation time).
>> 6. Hypervisor should do this as fast as possible (DRM playback use case).
>> 7. All domains (including dom0) should be handled in the same way.
>
>
> +1 here. Same path for all domains means less code and you it will get
> tested more
Yep. But this is somewhat incompatible with current implementation, as
currently VM monitor mechanism is being used.

-- 
WBR Volodymyr Babchuk aka lorc [+380976646013]
mailto: vlad.babchuk@xxxxxxxxx

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