linux-kernel - Re: [Xen-devel] [Patch V3 14/15] xen: allow more than 512 GB of RAM for 64 bit pv-domains

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Message-ID: <5565EFE2.7050308@citrix.com>
Date:	Wed, 27 May 2015 17:25:06 +0100
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>,
	<david.vrabel@...rix.com>, <boris.ostrovsky@...cle.com>
Subject: Re: [Xen-devel] [Patch V3 14/15] xen: allow more than 512 GB of RAM
 for 64 bit pv-domains

On 20/04/15 06:23, Juergen Gross wrote:
> 64 bit pv-domains under Xen are limited to 512 GB of RAM today. The
> main reason has been the 3 level p2m tree, which was replaced by the
> virtual mapped linear p2m list. Parallel to the p2m list which is
> being used by the kernel itself there is a 3 level mfn tree for usage
> by the Xen tools and eventually for crash dump analysis. For this tree
> the linear p2m list can serve as a replacement, too. As the kernel
> can't know whether the tools are capable of dealing with the p2m list
> instead of the mfn tree, the limit of 512 GB can't be dropped in all
> cases.
> 
> This patch replaces the hard limit by a kernel parameter which tells
> the kernel to obey the 512 GB limit or not. The default is selected by
> a configuration parameter which specifies whether the 512 GB limit
> should be active per default for domUs (domain save/restore/migration
> and crash dump analysis are affected).
> 
> Memory above the domain limit is returned to the hypervisor instead of
> being identity mapped, which was wrong anyway.
> 
> The kernel configuration parameter to specify the maximum size of a
> domain can be deleted, as it is not relevant any more.

Something in this patch breaks the hvc console in my test domU.

kernel BUG at /local/davidvr/work/k.org/tip/drivers/tty/hvc/hvc_xen.c:153

Which suggests the hvc driver mapped the wrong console ring frame.

David
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