linux-kernel - Re: [PATCH 9/9] x86/iommu: use dma_ops_list in get_dma

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Message-ID: <20080929092917.GO27426@8bytes.org>
Date:	Mon, 29 Sep 2008 11:29:17 +0200
From:	Joerg Roedel <joro@...tes.org>
To:	Muli Ben-Yehuda <muli@...ibm.com>
Cc:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	joerg.roedel@....com, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, iommu@...ts.linux-foundation.org,
	dwmw2@...radead.org, amit.shah@...ranet.com, mingo@...hat.com
Subject: Re: [PATCH 9/9] x86/iommu: use dma_ops_list in get_dma_ops

On Mon, Sep 29, 2008 at 12:25:49PM +0300, Muli Ben-Yehuda wrote:
> On Sun, Sep 28, 2008 at 08:44:24PM +0200, Joerg Roedel wrote:
> 
> > Hmm, we should only call find_dma_ops_for_device() the first time a
> > dma api call is done (look into get_dma_ops). But I also thought
> > about how this lock can be avoided. In the real world it should not
> > be necessary because the dma_ops list is initialized before dma api
> > calls are done. But since there is now a register function which can
> > be called its safer this way. What do you think, are we still safe
> > enough without this lock?
> 
> We could be, if we add a check to the register function that verifies
> it isn't being called after DMAs have started. Something like:
> 
> in register:
> 
>   if (dma_started)
>     yell loudly
> 
> before PCI device initialization and after IOMMU initialization:
>   dma_started = true

Good idea. I will change this in my patchset, thanks.

Joerg

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