Re: [Xen-devel] HVMlite ABI specification DRAFT B + implementation outline

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Tue, 9 Feb 2016, Jan Beulich wrote:
> > In the case of the hardware domain, Xen has traditionally passed-through the
> > native ACPI tables to the guest. This is something that of course we still
> > want to do, but in the case of HVMlite Xen will have to make sure that
> > the data passed in the ACPI tables to the hardware domain contain the 
> > accurate
> > hardware description. This means that at least certain tables will have to
> > be modified/mangled before being presented to the guest:
> > 
> >  * MADT: the number of local APIC entries need to be fixed to match the 
> > number
> >          of vCPUs available to the guest. The address of the IO APIC(s) also
> >          need to be fixed in order to match the emulated ones that we are 
> > going
> >          to provide.
> > 
> >  * DSDT: certain devices reported in the DSDT may not be available to the 
> > guest,
> >          but since the DSDT is a run-time generated table we cannot fix it. 
> > In
> >          order to cope with this, a STAO table will be provided that should
> >          be able to signal which devices are not available to the hardware
> >          domain. This is in line with the Xen/ACPI implementation for ARM.
> 
> Will STAO be sufficient for everything that may need customization?
> I'm particularly worried about processor related methods in DSDT or
> SSDT, which - if we're really meaning to do as you say - would need
> to be limited (or extended) to the number of vCPU-s Dom0 gets.
> What's even less clear to me is how you mean to deal with P-, C-,
> and (once supported) T-state management for CPUs which don't
> have a vCPU equivalent in Dom0.

It is possible to use the STAO to hide entire objects, including
processors, from the DSDT, which should be good enough to prevent dom0
from calling any of the processor related methods you are referreing to.
Then we can let Xen do cpuidle and cpufreq as it is already doing.

Would that work? Or do we still need Dom0 to call any ACPI methods for
power management?

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