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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Date:	Wed, 27 May 2015 18:05:59 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	David Vrabel <david.vrabel@...rix.com>,
	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: [Xen-devel] [Patch V3 14/15] xen: allow more than 512 GB of RAM
 for 64 bit pv-domains

On 27/05/15 17:25, David Vrabel wrote:
> 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.

Sorry, it's patch #13 (xen: move p2m list if conflicting with e820 map)
that seems to be bad.

David
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