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Re: [Xen-devel] why would XENMEM_decrease_reservation fail?

To: James Harper <james.harper@xxxxxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] why would XENMEM_decrease_reservation fail?
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Tue, 17 Nov 2009 03:34:35 +0000
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Thread-topic: [Xen-devel] why would XENMEM_decrease_reservation fail?
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On 16/11/2009 22:52, "James Harper" <james.harper@xxxxxxxxxxxxxxxx> wrote:

> I am attempting to implement the kludge to make save/restore/migrate
> work in the GPLPV drivers under Xen 3.4.1. On my test box I successfully
> free grant_table_pages + 1 pages. The logs from another users system
> show that each call to XENMEM_decrease_reservation returns 0 instead of
> 1.
> Under what circumstances would XENMEM_decrease_reservation fail? The pfn
> passed to XENMEM_decrease_reservation looks reasonable (similar values
> to my test box), and everything else is identical.

Really it should only fail if the page does not belong to the guest. You
might have to give them a patch to add tracing to error paths in e.g.,
guest_remove_page() to find out what's going on, if this happens
deterministically for them.

 -- Keir

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