linux-kernel - Re: [PATCH 0/3] fix GART to respect device's dma

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Date:	Tue, 16 Sep 2008 17:52:11 +0200
From:	Joerg Roedel <joerg.roedel@....com>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
CC:	andi@...stfloor.org, mingo@...e.hu, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] fix GART to respect device's dma_mask about virtual mappings

On Tue, Sep 16, 2008 at 10:20:40PM +0900, FUJITA Tomonori wrote:
> On Tue, 16 Sep 2008 02:54:32 +0200
> Andi Kleen <andi@...stfloor.org> wrote:
> 
> > FUJITA Tomonori <fujita.tomonori@....ntt.co.jp> writes:
> > 
> > > Currently, gart IOMMU ignores device's dma_mask when it does virtual
> > > mappings. So it could give a device a virtual address that the device
> > > can't access to.
> > 
> > Huh? That is what the need_iommu() logic in gart_map_sg()
> > does. An I'm not aware of any bugs in this area.
> 
> What the need_iommu() does is seeing if GART needs to do virtual
> mappings or not.
> 
> (After need_iommu() checking) What this patchset does is to guarantee
> that GART provides a virtual address that a device can access to.
> 
> 
> > Did you actually see that failure in practice? I don't see
> > how it could happen.
> 
> No, I did not. This patchset does the right thing theoretically, I
> think, but if such problem never happens for GART, I'll drop the patch
> for GART. Joerg?

I am not aware of any failures which are fixed by these patches. But in
theory there could be failures.

Joerg

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