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Date: Fri, 16 Mar 2007 10:02:23 -0700
From: Jeremy Fitzhardinge <jeremy@goop.org>
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To: Ingo Molnar <mingo@elte.hu>
CC: Andi Kleen <ak@muc.de>, Andrew Morton <akpm@linux-foundation.org>,
       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>, Rusty Russell <rusty@rustcorp.com.au>
Subject: Re: [patch 21/26] Xen-paravirt_ops: Use the hvc console infrastructure
 for Xen console
References: <20070301232443.195603797@goop.org> <20070301232528.926984984@goop.org> <20070316085451.GE23174@elte.hu>
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Ingo Molnar wrote:
>> +	prod = intf->in_prod;
>> +	mb();
>> +	BUG_ON((prod - cons) > sizeof(intf->in));
>>     
>
> such mb()'s are typically a sign of "i have no clear idea what SMP 
> serialization rules apply here, but something is needed because 
> otherwise it breaks" ?

Hm, in this case its because it's sharing the memory with Xen, so
there's a particular ordering protocol.  It needs some comments.

    J