Re: [PATCH v5 23/23] KVM: arm64: GICv4.1: Expose HW-based SGIs in debugfs

[Zenghui Yu]

Hi Marc,

On 2020/3/20 19:46, Marc Zyngier wrote:
> > > Side note: it'd be good to know what the rules are for your own GICv4
> > > implementations, so that we can at least make sure the current code 
> > > is safe.
> >
> > As far as I know, there will be some clean and invalidate operations
> > when v4.0 VPENDBASER.Valid gets programmed.
>
> Interesting. The ideal behaviour would be that the VPT is up-to-date and
> the caches clean when Valid is cleared (and once Dirty flips to 0).
>
> > But not sure about behaviors
> > on VMAPP (unmap), it may be a totally v4.1 stuff. I'll have a talk with
> > our SOC team.
>
> The VMAPP stuff is purely v4.1.
>
> > But how can the current code be unsafe? Is anywhere in the current code
> > will peek/poke the vpt (whilst GIC continues writing things into it)?
>
> No. But on VM termination, the memory will be freed, and will eventually be
> reallocated. If the GIC can still write to that memory after it has been
> freed, you end-up with memory corruption... Which is why I'm curious of
> what ensures that on your implementation.

Ah, I got it. I will check it with HiSilicon people next week and go
back to you if the code becomes unsafe due to the incomplete GICv4.


Thanks,
Zenghui