Re: [PATCH 1/2] xen/arm: Add imx8q{m,x} platform glue

[Julien Grall <julien@xxxxxxx>]

On 31/01/2024 15:32, John Ernberg wrote:
> Hi Julien,
Hi John,

> On 1/31/24 13:22, Julien Grall wrote:
> > Hi,
> >
> > On 31/01/2024 11:50, John Ernberg wrote:
> > > When using Linux for dom0 there are a bunch of drivers that need to do
> > > SMC
> > > SIP calls into the PSCI provider to enable certain hardware bits like the
> > > watchdog.
> > Do you know which protocol this is under the hood. Is this SCMI?
> I think I confused myself here when I wrote the commit log.
>
> The EL3 code in our case is ATF, and it does not appear to be SCMI, nor
> PSCI. The register usage of these SMC SIP calls are as follows:
> a0 - service
> a1 - function
> a2-a7 - args
>
> In ATF the handler is declared as a runtime service.
>
> Would the appropriate commmit message here be something along the lines
> of below?
> """
> When using Linux for dom0 there are a bunch of drivers that need to do   SMC
> SIP calls into the firmware to enable certain hardware bits like the
> watchdog.
> """
It reads better thanks.

[...]

> > But even if we restrict to dom0, have you checked that none of the SMCs
> > use buffers?
> I haven't found any such instances in the Linux kernel where a buffer is
> used. Adding a call filtering like suggested below additions of such
> functions can be discovered and adapted for if they would show up later.
> > Rather than providing a blanket forward, to me it sounds more like you
> > want to provide an allowlist of the SMCs. This is more futureproof and
> > avoid the risk to expose unsafe SMCs to any domain.
> >
> > For an example, you can have a look at the EEMI mediator for Xilinx.
> Ack. Do you prefer to see only on SMCCC service level or also on
> function level? (a1 register, per description earlier)
I am not sure. It will depend on whether it is correct to expose *all* 
the functions within a service level and they have the same format.
If you can't guarantee that, then you will most likely need to allowlist 
at the function level.
Also, do you have a spec in hand that would help to understand which 
service/function is implemented via those SMCs?
Cheers,

--
Julien Grall