linux-kernel - Re: [QUERY] lguest64

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Date:	Mon, 5 Aug 2013 12:50:40 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Gleb Natapov <gleb@...hat.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Mukesh Rathor <mukesh.rathor@...cle.com>,
	Mike Rapoport <mike.rapoport@...il.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Ramkumar Ramachandra <artagnon@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	xen-devel@...ts.xensource.com
Subject: Re: [QUERY] lguest64

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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