Re: [Xen-devel] [QUERY] lguest64

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Sun, Aug 04, 2013 at 03:37:08PM +0300, Gleb Natapov wrote:
> On Fri, Aug 02, 2013 at 03:09:34PM -0400, Konrad Rzeszutek Wilk wrote:
> > On Wed, Jul 31, 2013 at 06:25:04AM -0700, H. Peter Anvin wrote:
> > > On 07/31/2013 06:17 AM, Konrad Rzeszutek Wilk wrote:
> > > >>
> > > >> The big problem with pvops is that they are a permanent tax on future
> > > >> development -- a classic case of "the hooks problem."  As such it is
> > > >> important that there be a real, significant, use case with enough users
> > > >> to make the pain worthwhile.  With Xen looking at sunsetting PV support
> > > >> with a long horizon, it might currently be possible to remove pvops 
> > > >> some
> > > > 
> > > > PV MMU parts specifically.
> > > > 
> > > 
> > > Pretty much stuff that is driverized on plain hardware doesn't matter.
> > > What are you looking at with respect to the basic CPU control state?
> > 
> > 
> > CC-ing Mukesh here.
> > 
> > Let me iterate down what the experimental patch uses:
> > 
> >          struct pv_init_ops pv_init_ops;                                    
> >      
> >             [still use xen_patch, but I think that is not needed anymore]
> > 
> >          struct pv_time_ops pv_time_ops;                                    
> >      
> >             [we need that as we are using the PV clock source]
> > 
> >          struct pv_cpu_ops pv_cpu_ops;                                      
> >      
> >             [only end up using cpuid. This one is a tricky one. We could
> >              arguable remove it but it does do some filtering - for example
> >              THERM is turned off, or MWAIT if a certain hypercall tells us 
> > to
> >              disable that. Since this is now a trapped operation this could 
> > be
> >              handled in the hypervisor - but then it would be in charge of
> >              filtering certain CPUID - and this is at bootup - so there is 
> > not
> >              user interaction. This needs a bit more of thinking]
> > 
> read_msr/write_msr in this one make all msr accesses safe. IIRC there
> are MSRs that Linux uses without checking cpuid bits.
> IA32_PERF_CAPABILITIES for instance is used without checking PDCM bit.

Right, those are needed as well. Completly forgot about them.
> 
> 
> --
>                       Gleb.

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