linux-kernel - Re: [PATCH v1 2/2] nvme-pci: Fix iommu map (via swiotlb) failures when PAGE

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Date: Wed, 14 Feb 2024 18:36:38 -0700
From: Keith Busch <kbusch@...nel.org>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: sagi@...mberg.me, hch@....de, axboe@...nel.dk, will@...nel.org,
	joro@...tes.org, robin.murphy@....com, jgg@...dia.com,
	linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org,
	iommu@...ts.linux.dev, murphyt7@....ie, baolu.lu@...ux.intel.com
Subject: Re: [PATCH v1 2/2] nvme-pci: Fix iommu map (via swiotlb) failures
 when PAGE_SIZE=64KB

On Tue, Feb 13, 2024 at 10:09:19PM -0800, Nicolin Chen wrote:
> On Tue, Feb 13, 2024 at 04:31:04PM -0700, Keith Busch wrote:
> > On Tue, Feb 13, 2024 at 01:53:57PM -0800, Nicolin Chen wrote:
> > > @@ -2967,7 +2967,7 @@ static struct nvme_dev *nvme_pci_alloc_dev(struct pci_dev *pdev,
> > >               dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(48));
> > >       else
> > >               dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(64));
> > > -     dma_set_min_align_mask(&pdev->dev, NVME_CTRL_PAGE_SIZE - 1);
> > > +     dma_set_min_align_mask(&pdev->dev, PAGE_SIZE - 1);
> > >       dma_set_max_seg_size(&pdev->dev, 0xffffffff);
> > 
> > I recall we had to do this for POWER because they have 64k pages, but
> > page aligned addresses IOMMU map to 4k, so we needed to allow the lower
> > dma alignment to efficiently use it.
> 
> Thanks for the input!
> 
> In that case, we might have to rely on iovad->granule from the
> attached iommu_domain:

I explored a bit more, and there is some PPC weirdness that lead to
NVME_CTRL_PAGE_SIZE, I don't find the dma min align mask used in that
path. It looks like swiotlb is the only user for this, so your original
patch may be just fine.