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

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Message-ID: <544E61DD.8050305@citrix.com>
Date:	Mon, 27 Oct 2014 15:16:45 +0000
From:	David Vrabel <david.vrabel@...rix.com>
To:	Juergen Gross <jgross@...e.com>, <linux-kernel@...r.kernel.org>,
	<xen-devel@...ts.xensource.com>, <konrad.wilk@...cle.com>,
	<boris.ostrovsky@...cle.com>
Subject: Re: [PATCH 0/2] xen: Switch to virtual mapped linear p2m list

On 27/10/14 14:52, Juergen Gross wrote:
> Paravirtualized kernels running on Xen use a three level tree for
> translation of guest specific physical addresses to machine global
> addresses. This p2m tree is used for construction of page table
> entries, so the p2m tree walk is performance critical.
> 
> By using a linear virtual mapped p2m list accesses to p2m elements
> can be sped up while even simplifying code. To achieve this goal
> some p2m related initializations have to be performed later in the
> boot process, as the final p2m list can be set up only after basic
> memory management functions are available.

What impact does this have on 32-bit guests which don't have huge amount
of virtual address space?

I think a 32-bit guest could have up to 64 GiB of PFNs, which would
require a 128 MiB p2m array, which is too large?

David
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