linux-kernel - Re: [Xen-devel] [RFC][PATCH 03/10] xen/hybrid: Xen Hybrid Extension initialization

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Date:	Thu, 17 Sep 2009 07:22:44 +0100
From:	Keir Fraser <keir.fraser@...citrix.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Sheng Yang <sheng@...ux.intel.com>
CC:	Jeremy Fitzhardinge <Jeremy.Fitzhardinge@...rix.com>,
	xen-devel <xen-devel@...ts.xensource.com>,
	Eddie Dong <eddie.dong@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jun Nakajima <jun.nakajima@...el.com>
Subject: Re: [Xen-devel] [RFC][PATCH 03/10] xen/hybrid: Xen Hybrid Extension
 initialization

On 16/09/2009 21:24, "Jeremy Fitzhardinge" <jeremy@...p.org> wrote:

>> Guest would detect Hybrid capability using CPUID 0x40000002.edx, then call
>> HVMOP_enable_hybrid hypercall to enable hybrid support in hypervisor.
>>   
> 
> I think having an option to put PV guests into an HVM container is a
> good one, but as I mentioned in the other mail, I don't think this is
> the right approach.
> 
> It would be much better to make it so that an unmodified guest works in
> such a mode; even with no specific optimisations the guest would get
> benefit from faster kernel<->usermode switches.

By unmodified you mean ordinary PV guest? It's an interesting comparison --
PVing an HVM guest, versus HVMing (to some extent) a PV guest.

 -- Keir

> Then we can add specific optimisations to take advantage of, say,
> running in ring 0 (=fast syscalls) and having access to HAP hardware
> (=direct pagetable updates, no pinning).


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