On Mon, 17 Nov 2008 10:02:59 +0100 Ingo Molnar <mingo@xxxxxxx> wrote: > > * FUJITA Tomonori <fujita.tomonori@xxxxxxxxxxxxx> wrote: > > > On Mon, 17 Nov 2008 09:15:26 +0100 > > Ingo Molnar <mingo@xxxxxxx> wrote: > > > > > > > > * FUJITA Tomonori <fujita.tomonori@xxxxxxxxxxxxx> wrote: > > > > > > > This patch fixes swiotlb to use dev->coherent_dma_mask in > > > > alloc_coherent. Currently, swiotlb uses dev->dma_mask in > > > > alloc_coherent but alloc_coherent is supposed to use > > > > coherent_dma_mask. It could break drivers that uses smaller > > > > coherent_dma_mask than dma_mask (though the current code works for > > > > the majority that use the same mask for coherent_dma_mask and > > > > dma_mask). > > > > > > > > Signed-off-by: FUJITA Tomonori <fujita.tomonori@xxxxxxxxxxxxx> > > > > --- > > > > lib/swiotlb.c | 10 +++++++--- > > > > 1 files changed, 7 insertions(+), 3 deletions(-) > > > > > > Applied it with the changelog below to tip/core/urgent, thanks! > > > > > > I also flagged it for v2.6.28 inclusion. This bug was caused by the > > > removal of the GFP_DMA hack in swiotlb_alloc_coherent() in this cycle. > > > I havent seen it actually reported anywhere - have you perhaps?Or have > > > you found this via code review? > > > > This wasn't introduced by the removal of the GFP_DMA hack. It has > > been for ages, I think. > > Yeah, what i mean is that our GFP_DMA hack (which we indeed had for > years) definitely _hid_ the problem: on x86 for example it limits > coherent DMA buffers into the DMA zone: the first 16 MB of RAM. Ah, I see. I misunderstood what you meant. > ( Other platforms are pretty narrow about GFP_DMA too - it implies at > least DMA32 which is in practice often the real limit for > cache-coherent DMA addresses. ) > > So the removal of GFP_DMA flag from coherent allocations exposed us to > this long-standing (but hidden) problem. Yes, you are right. But it's pretty hard to hit this bug since x86_64 rarely uses swiotlb_alloc_coherent. pci-swiotlb_64.c tries dma_generic_alloc_coherent first and then, only if it fails, it uses swiotlb_alloc_coherent. dma_generic_alloc_coherent usually succeeds. Before removing the GFP_DMA hack (the dma_alloc_coherent rewrite), x86_64 rarely used swiotlb_alloc_coherent too because swiotlb_alloc_coherent was used only if dma_alloc_coherent fails. This issue was hidden by dma_alloc_coherent and GFP_DMA hack. -- To unsubscribe from this list: send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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