Re: [PATCH 06/25] xen: Core Xen implementation

[Keir Fraser]

On 27/4/07 08:08, "Jeremy Fitzhardinge" <jeremy@xxxxxxxx> wrote:

>> Don't you need a rmb() here then? The CPU could speculate reads
>> (more occurrences)
>>   
> 
> Is rmb() sufficient?  It will stop a speculative read on the pending
> flag, but will it make sure the write has happened by then?  Ie, is it a
> write-vs-read barrier, or just a read-vs-read?
> Documentation/memory-barriers.txt suggests not.

The barrier() is sufficient. We are racing against Xen checking
evtchn_upcall_mask *on the local cpu*. Which means an interrupt has to
occur, which squashes speculative stuff.

Yeah, I know, it needs a better comment. :-)

 -- Keir


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