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[Xen-devel] Re: [patch 21/26] Xen-paravirt_ops: Use the hvc console infr

To: Ingo Molnar <mingo@xxxxxxx>
Subject: [Xen-devel] Re: [patch 21/26] Xen-paravirt_ops: Use the hvc console infrastructure for Xen console
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Fri, 16 Mar 2007 10:02:23 -0700
Cc: Zachary Amsden <zach@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, virtualization@xxxxxxxxxxxxxx, Rusty Russell <rusty@xxxxxxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, Chris Wright <chrisw@xxxxxxxxxxxx>, Andi Kleen <ak@xxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
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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


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