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

[Julien Grall <julien.grall@xxxxxxx>]

On 01/03/17 14:13, Volodymyr Babchuk wrote:
> Hi, Julien
Hi Volodymyr,

> 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?
I will chat internally about it and come back to you.

> > > 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.
I am not sure to understand here. Can you detail it?

Cheers,

--
Julien Grall

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