linux-kernel - Re: [GIT PULL] AMD IOMMU updates for 2.6.28-rc5

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Date:	Wed, 19 Nov 2008 10:36:11 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Joerg Roedel <joro@...tes.org>
Cc:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	joerg.roedel@....com, iommu@...ts.linux-foundation.org,
	mingo@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [GIT PULL] AMD IOMMU updates for 2.6.28-rc5


* Joerg Roedel <joro@...tes.org> wrote:

> We can't test all drivers for those bugs until 2.6.28 will be 
> released. And these bugs can corrupt data, for example when a driver 
> frees dma addresses allocated by another driver and these addresses 
> are then reallocated.
>
> The only way to protect the drivers from each other is to isolate 
> them in different protection domains. The AMD IOMMU driver prints a 
> WARN_ON() if a driver frees dma addresses not yet mapped. This 
> triggered with the bnx2 and the ixgbe driver.
>
> And the data corruption is real, it eat the root-fs of my testbox 
> one time.

a WARN_ON() can be acted upon much easier than silent/spurious data 
corruption. So printing a WARN_ON() will result in drivers being fixed 
a lot faster (and with a lot less debugging needed) than if we were 
intentionally letting DMA corruption happen. The WARN_ON() will be 
routed to kerneloops.org on the major distros, etc. etc.

> I agree that we need to fix the drivers. I plan to implement some 
> debug code which allows driver developers to detect those bugs even 
> if they have no IOMMU in the system.

That would be _really_ nice to have.

	Ingo
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