Subject: Re: [PATCH 26/26] KVM: PPC: Add Documentation about PV interface

From: Avi Kivity <[email-masked]>
Date: Sun, 27 Jun 2010 11:34:06 +0300

On 06/26/2010 02:25 AM, Alexander Graf wrote:
> We just introduced a new PV interface that screams for documentation. So here
> it is - a shiny new and awesome text file describing the internal works of
> the PPC KVM paravirtual interface.
>
>
> +Querying for existence
> +======================
> +
> +To find out if we're running on KVM or not, we overlay the PVR register. Usually
> +the PVR register contains an id that identifies your CPU type. If, however, you
> +pass KVM_PVR_PARA in the register that you want the PVR result in, the register
> +still contains KVM_PVR_PARA after the mfpvr call.
> +
> +	LOAD_REG_IMM(r5, KVM_PVR_PARA)
> +	mfpvr	r5
> +	[r5 still contains KVM_PVR_PARA]
> +
> +Once determined to run under a PV capable KVM, you can now use hypercalls as
> +described below.
>    

On x86 we allow host userspace to determine whether the guest sees the 
paravirt interface (and what features are exposed).  This allows you to 
live migrate from a newer host to an older host, by not exposing the 
newer features.

-- 
error compiling committee.c: too many arguments to function