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

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Message-ID: <544F902C.8040502@citrix.com>
Date:	Tue, 28 Oct 2014 12:46:36 +0000
From:	Andrew Cooper <andrew.cooper3@...rix.com>
To:	David Vrabel <david.vrabel@...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 12:44, David Vrabel wrote:
> 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).

Ah - fine (if that is how it works).

~Andrew
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