Re: [PATCH 0/2] expose host-phys-bits to guest

[Xiaoyao Li]

On 9/1/2022 9:58 PM, Gerd Hoffmann wrote:

> > Anyway, IMO, guest including guest firmware, should always consult from
> > CPUID leaf 0x80000008 for physical address length.
>
> It simply can't for the reason outlined above.  Even if we fix qemu
> today that doesn't solve the problem for the firmware because we want
> backward compatibility with older qemu versions.  Thats why I want the
> extra bit which essentially says "CPUID leaf 0x80000008 actually works".

I don't understand how it backward compatible with older qemu version. 
Old QEMU won't set the extra bit you introduced in this series, and all 
the guest created with old QEMU will become untrusted on CPUID leaf 
0x80000008 ?

> take care,
>    Gerd