Hi,
> > diff --git a/target/i386/cpu.h b/target/i386/cpu.h
> > index 952174bb6f52..d427218827f6 100644
> > --- a/target/i386/cpu.h
> > +++ b/target/i386/cpu.h
> > + guest_phys_bits = kvm_get_guest_phys_bits(cs->kvm_state);
> > + if (guest_phys_bits &&
> > + (cpu->guest_phys_bits == 0 ||
> > + cpu->guest_phys_bits > guest_phys_bits)) {
> > + cpu->guest_phys_bits = guest_phys_bits;
> > + }
>
> Like Xiaoyao mentioned, the right place for this is kvm_cpu_realizefn,
> after host_cpu_realizefn returns. It should also be conditional on
> cpu->host_phys_bits.
Ok.
> It also makes sense to:
>
> - make kvm_get_guest_phys_bits() return bits 7:0 if bits 23:16 are zero
>
> - here, set cpu->guest_phys_bits only if it is not equal to
> cpu->phys_bits (this undoes the previous suggestion, but I think it's
> cleaner)
Not sure about that.
I think it would be good to have a backward compatibility story.
Currently neither the kernel nor qemu set guest_phys_bits. So if the
firmware finds guest_phys_bits == 0 it does not know whenever ...
(a) kernel or qemu being too old, or
(b) no restrictions apply, it is safe to go with phys_bits.
One easy option would be to always let qemu pass through guest_phys_bits
from the kernel, even in case it is equal to phys_bits.
> - add a property in x86_cpu_properties[] to allow configuration with TCG.
Was thinking about configuration too. Not sure it is a good idea to
add yet another phys-bits config option to the mix of options we already
have ...
In case host_phys_bits=true qemu could simply use
min(kernel guest-phys-bits,host-phys-bits-limit)
For the host_phys_bits=false case it would probably be best to just
not set guest_phys_bits.
take care,
Gerd
