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Date: Thu, 15 Feb 2007 22:52:29 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Andi Kleen <ak@muc.de>, linux-kernel@vger.kernel.org,
       virtualization@lists.osdl.org, xen-devel@lists.xensource.com,
       Chris Wright <chrisw@sous-sol.org>, Zachary Amsden <zach@vmware.com>,
       Ian Pratt <ian.pratt@xensource.com>,
       Christian Limpach <Christian.Limpach@cl.cam.ac.uk>
Subject: Re: [patch 18/21] Xen-paravirt: Add Xen grant table support
Message-Id: <20070215225229.6b63d050.akpm@linux-foundation.org>
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	<20070216022531.904462260@goop.org>
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On Thu, 15 Feb 2007 18:25:07 -0800 Jeremy Fitzhardinge <jeremy@goop.org> wrote:

> +int gnttab_grant_foreign_access(domid_t domid, unsigned long frame,
> +				int readonly)
> +{
> +	int ref;
> +
> +	if (unlikely((ref = get_free_entry()) == -1))
> +		return -ENOSPC;
> +
> +	shared[ref].frame = frame;
> +	shared[ref].domid = domid;
> +	wmb();
> +	shared[ref].flags = GTF_permit_access | (readonly ? GTF_readonly : 0);
> +
> +	return ref;
> +}
> +EXPORT_SYMBOL_GPL(gnttab_grant_foreign_access);

We have lots of open-coded mysteriously unexplained barriers in here.

I assume they're not smp_wmb() because this could be a !SMP guest talking
to an SMP host?