Re: [Xen-devel] [PATCH v2 3/3] paravirt: rename paravirt_enabled to paravirt_legacy

[Boris Ostrovsky]

On 02/08/2016 11:26 AM, Andrew Cooper wrote:
> On 08/02/16 16:12, Boris Ostrovsky wrote:
> > On 02/08/2016 11:05 AM, Andrew Cooper wrote:
> > > For compatibility with other virtualisation specs, Xen's cpuid leaves
> > > shift depending on configuration.
> > >
> > > Spec at
> > > http://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=xen/include/public/arch-x86/cpuid.h;h=d709340f18d089560b959835eabb7b6609542c7e;hb=HEAD#l33
> > >
> > >
> > > Basically, they are either at 0x40000000, or 0x40000100 if viridian or
> > > vmware compatibility has been enabled.
> > (Also in arch/x86/include/asm/xen/cpuid.h in Linux tree).
> The other complication is that, for a PV guest, you must use the forced
> emulation prefix for the cpuid instruction to trap into the hypervisor.
>
> This either means you must be sure you are under Xen to start with, or
> use an extable entry to catch the #UD fault if you are not under Xen.

I think we are OK for PV because this code will be executed after pvops 
are set and so we will be calling xen_cpuid().

-boris