linux-kernel - Re: swiotlb_alloc_coherent: allocated memory is out of range for device

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Date:	Wed, 22 Oct 2008 22:19:33 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	fujita.tomonori@....ntt.co.jp
Cc:	tiwai@...e.de, svens@...ckframe.org, joerg.roedel@....com,
	mingo@...e.hu, linux-kernel@...r.kernel.org
Subject: Re: swiotlb_alloc_coherent: allocated memory is out of range for
 device

On Wed, 22 Oct 2008 22:13:39 +0900
FUJITA Tomonori <fujita.tomonori@....ntt.co.jp> wrote:

> > > > So, even adding GFP_DMA works mostly, it has still potentially
> > > > breakage when you can't get the page and fall back to iotlb pages,
> > > > just like the panic above.
> > > > 
> > > > Also, the removal of GFP_DMA hack is a bad idea.  For example, if a
> > > > device requires 28bit DMA mask, it doesn't set always GFP_DMA for
> > > > allocation because pages in ZONE_NORMAL may be inside that DMA mask.
> > > > Normal allocators allow this behavior but swiotlb allocator doesn't.
> > > > (Correct me if I'm wrong here -- I haven't followed much the recent
> > > >  changes.)
> > > 
> > > 28bit DMA mask is supposed to be handled properly. Firstly, we try
> > > with DMA_32BIT_MASK and if an allocated address is not fit for 28bit
> > > mask, we try GFP_DMA again.
> > 
> > Yep, dma_generic_alloc_coherent() works like that for ages.
> > My point is about swiotlb_alloc_coherent(), and I don't see the
> > relevant code there...
> 
> Oops, you are right. swiotlb doesn't try again with GFP_DMA now. Joerg
> changed the GFP_DMA retry mechanism work only for pci-nommu.c It broke
> GART IOMMU and x86's swiotlb. I modified dma_generic_alloc_coherent to
> work with pci-nommu and GART. I promised Ingo to fix swiotlb too but I
> forgot about it.
> 
> Sorry, I'll fix this soon but your case (28bit mask) is supposed to

Oops, I meant, 24bit mask, as you know.


> work without the GFP_DMA retry mechanism. As I wrote above, I suspect
> that dma flag is not set correctly.
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