Re: [Qemu-ppc] [Qemu-devel] [RFC PATCH v3] powerpc: add PVR mask support

[Anthony Liguori]

On Thu, Aug 15, 2013 at 7:20 PM, Benjamin Herrenschmidt
<address@hidden> wrote:
> On Thu, 2013-08-15 at 16:47 +0200, Andreas Färber wrote:
>> comparing values for closest match. So that if you have a v2.4 and QEMU
>> knows v2.1 and v2.3 we take v2.3 and fill in the v2.4 PVR.
>
> Another thing to keep in mind is that we will want eventually to support
> POWER7 compatibility more on POWER8 with HV KVM. I am not certain what
> the "right" way to do it via qemu command line is, whether we would
> have a -cpu entry (-cpu POWER7_COMPAT ?) or such...

But this doesn't change the hardware PVR value right, just the virtual
PVR that's in the device tree?  Maybe you need to change some state of
the virtual VCPU but from a QEMU point of view, it's still a POWER8
VCPU (it's just in power7 compat mode).

> Additionally, the trick here is that qemu must be able to change its model
> at runtime (a reset is permitted). This is how PAPR defines the 
> reconfiguration
> reboot (for that and other things).

I don't think the model changes.  It's just a flag in the power8 vcpu state.

No different IMHO between jumping from real mode to protected mode to
long mode on x86.

Regards,

Anthony Liguori

> IE. The guest kernel will call FW early on, while still operating under
> OFW (from prom_init) indicating what it supports, and if that doesn't include
> P8, we need to reconfigure the CPU model to be P7 compat (we are allowed to
> reboot and reload the same kernel, which is generally what pHyp does, but
> we'd like to try avoiding it as much as possible).
>
> Cheers,
> Ben.
>
>
>