Re: [RFC v2 00/14] Add SDEI support for arm64

[Heyi Guo]

Hi Marc,

On 2020/2/5 21:15, Marc Zyngier wrote:
> Hi Heyi,
>
> On 2020-02-04 08:26, Heyi Guo wrote:
> > Update Marc's email address.
> >
> > +cc Gavin as he is posting a RFC for ARM NMI.
> >
> > Hi Marc,
> >
> > Really sorry for missing to update your email address, for the initial
> > topic was raised long time ago and I forgot to update the Cc list in
> > the commit message of the patches.
> >
> > Thanks Gavin for forwarding current discussion on ARM NMI to me.
> >
> > For you said SDEI is "horrible", does it mean we'd better never
> > implement SDEI in virtual world? Or do you have any advice on how to
> > implement it?
>
> My concern is that SDEI implies having EL3. EL3 not being virtualizable
> with KVM, you end-up baking SDEI in *hardware*. Of course, this hardware
> is actually software (it is QEMU), but this isn't the way it was 
> intended.

> It's not the first time we've done that (PSCI is another example), but 
> the
> logic behind SDEI looks much more invasive.

Thanks for your comments.

Thinking about them for quite a while, below is my understanding, please 
correct me if I'm wrong:

So should the KVM based virtual machine be treated as one with CPUs only 
having NS-EL1 and NS-EL0, ideally? And SDEI messes up this model, isn't it?

PSCI only contains some one-shot operations, so it is much less invasive 
than SDEI.


I've another question. The origin of "virtual" SDEI requirement comes 
from the lack of hard lockup detector in VM. We can have some kind of 
watchdog, but how can the watchdog trigger the VM OS to panic and run 
kdump, even in irq-off state?

Thanks,

Heyi

>         M.