Date: Wed, 19 Nov 2008 10:36:11 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Joerg Roedel <joro@8bytes.org>
Cc: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>, joerg.roedel@amd.com,
       iommu@lists.linux-foundation.org, mingo@redhat.com,
       linux-kernel@vger.kernel.org
Subject: Re: [GIT PULL] AMD IOMMU updates for 2.6.28-rc5
Message-ID: <20081119093611.GF22309@elte.hu>
References: <20081118154322.GX13394@amd.com> <20081119150504G.fujita.tomonori@lab.ntt.co.jp> <20081119092544.GD29705@8bytes.org>
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* Joerg Roedel <joro@8bytes.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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