Re: [Qemu-devel] [RFC PATCH v3 3/4] hw/intc/arm_gicv3_kvm: Implement get/put functions

[Pavel Fedin]

 Hello!

> > +            reg = c->pendbaser & (GICR_PENDBASER_OUTER_CACHEABILITY_MASK |
> > +                                  GICR_PENDBASER_ADDR_MASK |
> > +                                  GICR_PENDBASER_SHAREABILITY_MASK |
> > +                                  GICR_PENDBASER_CACHEABILITY_MASK);
> > +            if (!c->redist_ctlr & GICR_CTLR_ENABLE_LPIS) {
> > +                reg |= GICR_PENDBASER_PTZ;
> > +            }
> 
> Why does the state of the pendbaser register depend on state in the
> redist_ctlr ?

 PTZ bit is write-only, we cannot read it back. And spec says that setting PTZ 
is adviced while LPIs are not enabled, because it shortens down the time of GIC 
initialization. So, i had to implement this small heuristics here. Is this 
approach OK?

> Worth a comment, whatever the answer is.

 I will.

> > +            kvm_gicr_access(s, GICR_PENDBASER, ncpu, &reg, false);
> > +            c->pendbaser = reg & (GICR_PENDBASER_OUTER_CACHEABILITY_MASK |
> > +                                  GICR_PENDBASER_ADDR_MASK |
> > +                                  GICR_PENDBASER_SHAREABILITY_MASK |
> > +                                  GICR_PENDBASER_CACHEABILITY_MASK);
> 
> Why do we need to mask these values?

 I decided to do this at least for the case of KVM->TCG migration (as far as i 
understand, such things are possible). In this case i think we should not 
pollute our state with read-only bits, which get added by the emulation code 
itself.

> Do we not transfer ICC_SRE_EL1 because it's implemented as RO?
> (I think that's right for no-irq/fiq-bypass, sysregs only.)

 Yes, also because looks like KVM is not going to implement GICv3 with non-SRE 
mode, instead, if we want to run a legacy guest, we just configure our host to 
provide GICv2 for it.
 I actually migrate only those CPU interface registers, which are saved by the 
kernel code as part of guest's context.

Kind regards,
Pavel Fedin
Expert Engineer
Samsung Electronics Research center Russia