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[Xen-ia64-devel] Re: [XenPPC] Re: [Xen-devel] [PATCH] [GNTTAB] expandabl

To: Hollis Blanchard <hollisb@xxxxxxxxxx>
Subject: [Xen-ia64-devel] Re: [XenPPC] Re: [Xen-devel] [PATCH] [GNTTAB] expandable grant table
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Tue, 27 Feb 2007 07:50:41 +0000
Cc: xen-ppc-devel@xxxxxxxxxxxxxxxxxxx, Isaku Yamahata <yamahata@xxxxxxxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Keir Fraser <keir@xxxxxxxxxxxxx>, xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
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On 27/2/07 00:05, "Hollis Blanchard" <hollisb@xxxxxxxxxx> wrote:

> I don't believe that's a concern, since updating
> grant_table->nr_grant_frames is the very last step in
> gnttab_grow_table(), and it will only grow.

If there's a memory barrier before the update of nr_grant_frames, explicitly
or implied, then removing the locking from add_to_physmap is fine. Otherwise
not: reading an integer is atomic, but using that as a flag to indicate
presence of other state updated under the same lock is just a little bit
suspect (but might be okay).

 -- Keir



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