linux-kernel - Re: [PATCH] xen: adjust early dom0 p2m handling to xen hypervisor behavior

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Date:   Wed, 10 May 2017 16:19:56 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org
Subject: Re: [PATCH] xen: adjust early dom0 p2m handling to xen hypervisor
 behavior

On 10/05/17 15:45, Boris Ostrovsky wrote:
> On 05/10/2017 12:08 AM, Juergen Gross wrote:
>> When booted as pv-guest the p2m list presented by the Xen is already
>> mapped to virtual addresses. In dom0 case the hypervisor might make use
>> of 2M- or 1G-pages for this mapping. Unfortunately while being properly
>> aligned in virtual and machine address space, those pages might not be
>> aligned properly in guest physical address space.
> 
> Is this the only place where we shouldn't assume that large page is
> properly aligned (in pfn space)?

It is the only case requiring a change. xen_cleanmfnmap_*() already does
this correctly via the same mechanism I used in this patch.

I'm not aware of any other large pages set up by Xen for pv guests than
the ones for the initial p2m list. And these large pages are freed (via
xen_cleanmfnmap_*()) after setting up the final p2m list in kernel
virtual space.


Juergen