linux-kernel - Re: [Xen-devel] [PATCH 0/2] xen: Switch to virtual mapped linear p2m list

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Date:	Tue, 28 Oct 2014 12:44:43 +0000
From:	David Vrabel <david.vrabel@...rix.com>
To:	Andrew Cooper <andrew.cooper3@...rix.com>,
	Juergen Gross <jgross@...e.com>,
	Ian Campbell <Ian.Campbell@...rix.com>
CC:	<boris.ostrovsky@...cle.com>, <xen-devel@...ts.xensource.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH 0/2] xen: Switch to virtual mapped linear
 p2m list

On 28/10/14 12:42, Andrew Cooper wrote:
> On 28/10/14 12:39, David Vrabel wrote:
>> On 28/10/14 12:07, Juergen Gross wrote:
>>> Okay, back to the original question: is the (up to) 64 MB virtual
>>> mapping of the p2m list on 32-bit pv domains a problem or not?
>> I think up-to 64 MiB of vmalloc area is fine.  The vmalloc space can be
>> increased with a command line option in the unlikely event that there
>> are domUs that would be affected.
>>
>>> If yes, the virtual mapped linear p2m list could still be used on
>>> 64 bit domains, paving the way for support of more than 512 GB of
>>> domain memory. OTOH having to keep the p2m tree coding alive isn't
>>> my favorite solution...
>> Having to keep both the tree and linear p2m code would be awful.  Let's
>> not do this!
>>
>> David
> 
> How is the toolstack expected to find and mutate this p2m on migrate? 
> The toolstack does not use guest pagetables.

The p2m code maintains two trees.  One for use by the guest and one for
use by the toolstack.  This series replaces the first tree with the
linear array (at least that's how I understand it -- I've not reviewed
the series in detail yet).

David
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