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Date: Mon, 09 Nov 2009 23:02:27 +0000 From: David Woodhouse <dwmw2@...radead.org> To: FUJITA Tomonori <fujita.tomonori@....ntt.co.jp> Cc: alex.williamson@...com, iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org, akpm@...ux-foundation.org, Chris Wright <chrisw@...s-sol.org> Subject: Re: [PATCH] intel-iommu: Obey coherent_dma_mask for alloc_coherent on passthrough On Fri, 2009-11-06 at 11:41 +0900, FUJITA Tomonori wrote: > This is fine for 2.6.32 but we'll cleanly fix this by using > swiotlb_dma_ops later, right? Well, the idea was that with 'iommu=pt' we'd have passthrough mode for _decent_ devices, but the crappy devices without 64-bit DMA would just have the IOMMU enabled instead. We can see this as a simple classification bug -- we should be checking pdev->coherent_dma_mask as well as pdev->dma_mask: --- a/drivers/pci/intel-iommu.c +++ b/drivers/pci/intel-iommu.c @@ -2196,7 +2196,8 @@ static int iommu_should_identity_map(struct pci_dev *pdev, int startup) * take them out of the 1:1 domain later. */ if (!startup) - return pdev->dma_mask > DMA_BIT_MASK(32); + return (pdev->dma_mask & pdev->coherent_dma_mask) < + dma_get_required_mask(); return 1; } That fixes the case of a 32-bit coherent_dma_mask as it was intended to be fixed. Unfortunately, Alex's hardware is more broken than that. It also likes to do stray reads from unmapped addresses -- addresses which used to be mapped at some time in the past. So he really _does_ want the IOMMU disabled, or in passthrough mode. But I think that's a special case and needs to be handled with a quirk, while the above patch actually addresses the problem we claimed we were trying to address. Handling Alex's broken hardware probably wants to be done with 'iommu=off' for now, and then when Chris's swiotlb fallback patches are done we can perhaps do something more cunning. I'm slightly reluctant to put the half-arsed 'try to allocate in the right region for broken devices but without full swiotlb support' option into 2.6.32. -- David Woodhouse Open Source Technology Centre David.Woodhouse@...el.com Intel Corporation -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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