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 14:03:07 +0100
From:	Juergen Gross <jgross@...e.com>
To:	Andrew Cooper <andrew.cooper3@...rix.com>,
	David Vrabel <david.vrabel@...rix.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 10/28/2014 01:46 PM, Andrew Cooper wrote:
> 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).

That's the plan, yes.


Juergen

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