linux-kernel - Re: [Xen-devel] [RFC PATCH] Boot PV guests with more than 128GB (v1) for 3.7

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Message-ID: <1343384489.6812.143.camel@zakaz.uk.xensource.com>
Date:	Fri, 27 Jul 2012 11:21:29 +0100
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	Jan Beulich <JBeulich@...e.com>
CC:	Ian Jackson <Ian.Jackson@...citrix.com>,
	xen-devel <xen-devel@...ts.xen.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [RFC PATCH] Boot PV guests with more than 128GB
 (v1) for 3.7

On Fri, 2012-07-27 at 11:17 +0100, Jan Beulich wrote:
> >>> On 27.07.12 at 12:00, Ian Campbell <Ian.Campbell@...rix.com> wrote:
> > On Fri, 2012-07-27 at 08:34 +0100, Jan Beulich wrote:
> >> >>> On 26.07.12 at 22:47, Konrad Rzeszutek Wilk <konrad.wilk@...cle.com> wrote:
> >> >  2). Allocate a new array, copy the existing P2M into it,
> >> >     revector the P2M tree to use that, and return the old
> >> >     P2M to the memory allocate. This has the advantage that
> >> >     it sets the stage for using XEN_ELF_NOTE_INIT_P2M
> >> >     feature. That feature allows us to set the exact virtual
> >> >     address space we want for the P2M - and allows us to
> >> >     boot as initial domain on large machines.
> >> 
> >> And I would hope that the tools would get updated to recognize
> >> this note too, so that huge DomU-s would become possible as
> >> well.
> > 
> > Does this help us with >160GB 32 bit PV guests too? I'm guessing not
> > since the real limitation there is the relatively small amount of kernel
> > address space.
> 
> Correct - 32-bit PV guests are limited anyway (and it's for a
> reason the Dom0 support in the hypervisor only deals with
> 64-bit ones). And honestly, considering the huge page
> information table such a memory amount would require, I
> doubt this big a PV guest would even boot (or if it does, be
> of any use).

Right.

I was actually think of the issue with 32 bit PV guests accessing MFN
space > 160G, even if they are themselves small, which is a separate
concern.

Ian.

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