linux-kernel - Re: [PATCH v2 2/4] KVM: introduce "xinterface" API for external interaction with guests

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Message-ID: <4ACDFB1F.6040803@redhat.com>
Date:	Thu, 08 Oct 2009 16:45:51 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Gregory Haskins <gregory.haskins@...il.com>
CC:	Gregory Haskins <ghaskins@...ell.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	"alacrityvm-devel@...ts.sourceforge.net" 
	<alacrityvm-devel@...ts.sourceforge.net>,
	David Howells <dhowells@...hat.com>
Subject: Re: [PATCH v2 2/4] KVM: introduce "xinterface" API for external	interaction
 with guests

On 10/07/2009 02:48 PM, Gregory Haskins wrote:
>
>> If f() can cause another agent to write to p (by freeing
>> it to a global list, for example), then it is its responsibility to
>> issue the smp_rmb(), otherwise no calculation that took place before f()
>> and accessed p is safe.
>>
>>      
> IOW: David is right.  You need a cpu-barrier one way or the other.  We
> can either allow ->release() to imply one (and probably document it that
> way, like we did for slow-work), or we can be explicit.

No, ->release() must do it or it becomes impossible to program.  And in 
fact it will, to place the freed structure on a global list it must take 
a lock which implies an smp_rmb().

> I chose to be
> explicit since it is kind of self-documenting, and there is no need to
> be worried about performance since the release is slow-path.
>    

It's so self-documenting I had no idea what it was there for.

-- 
error compiling committee.c: too many arguments to function

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