Re: [PATCH v2 2/2] [RfC] expose host-phys-bits to guest

[Gerd Hoffmann]

  Hi,

> > @@ -424,7 +426,10 @@ static void microvm_device_pre_plug_cb(HotplugHandler 
> > *hotplug_dev,
> >  {
> >      X86CPU *cpu = X86_CPU(dev);
> >  
> > -    cpu->host_phys_bits = true; /* need reliable phys-bits */
> > +    /* need reliable phys-bits */
> > +    cpu->env.features[FEAT_KVM_HINTS] |=
> > +        (1 << KVM_HINTS_PHYS_ADDRESS_SIZE_DATA_VALID);
> > +
> 
> Do we need compat machinery for this?

Don't think so, microvm has no versioned machine types anyway.

> > --- a/target/i386/cpu.c
> > +++ b/target/i386/cpu.c

> >      [FEAT_KVM_HINTS] = {
> >          .type = CPUID_FEATURE_WORD,
> >          .feat_names = {
> > -            "kvm-hint-dedicated", NULL, NULL, NULL,
> > +            "kvm-hint-dedicated", "host-phys-bits", NULL, NULL,

> > -    DEFINE_PROP_BOOL("host-phys-bits", X86CPU, host_phys_bits, false),

> > -    if (cpu->host_phys_bits) {
> > +    if (cpu->env.features[FEAT_KVM_HINTS] &
> > +        (1 << KVM_HINTS_PHYS_ADDRESS_SIZE_DATA_VALID)) {
> >          /* The user asked for us to use the host physical bits */
> >          phys_bits = host_phys_bits;
> >          if (cpu->host_phys_bits_limit &&
> 
> I think we still want to key this one off host_phys_bits
> so it works for e.g. hyperv emulation too.

I think that should be the case.  The chunks above change the
host-phys-bits option from setting cpu->host_phys_bits to setting
the FEAT_KVM_HINTS bit.  That should also happen with hyperv emulation
enabled, and the bit should also be visible to the guest then, just at
another location (base 0x40000100 instead of 0x40000000).

take care,
  Gerd