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

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Date:	Thu, 20 Nov 2008 12:31:29 +0100
From:	Joerg Roedel <joerg.roedel@....com>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
CC:	joro@...tes.org, 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

On Thu, Nov 20, 2008 at 01:25:15PM +0900, FUJITA Tomonori wrote:
> On Wed, 19 Nov 2008 10:25:44 +0100
> Joerg Roedel <joro@...tes.org> wrote:
> > I found issues in network drivers only for now. The two drivers where I
> > found issues are the in-kernel ixgbe driver (I see IO_PAGE_FAULTS
> > there), the ixgbe version from the Intel website has a double-free bug
> > when unloading the driver or changing the device mtu. The same problem
> > was found with the Broadcom NetXtreme II driver.
> 
> I see, thanks. You already reported the bugs to netdev?
> 

Not yet, but I will do so when I can prove the bug is not in my driver
;) (== when my debug code is ready)

> > 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.
> 
> It would be better to add such WARN_ON to VT-d. VT-d is everywhere
> nowadays. I think that there are some developers who can test these
> drivers with VT-d.

Yes, I agree.

> > And the data corruption is real, it eat the root-fs of my testbox one
> > time.
> > 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.
> 
> It's not so hard to add such debug feature to swiotlb, I guess.
> 

Yes, but I prefer to have it outside of any dma_ops implementation. This
way it can also be used to find out if a bug originated from the device
driver or the dma_ops implementation.

Joerg

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