linux-kernel - Re: [PATCH] iommu/vt-d: Implement dma_[un]map

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Message-ID: <20190119094002.GA21653@lst.de>
Date:   Sat, 19 Jan 2019 10:40:02 +0100
From:   Christoph Hellwig <hch@....de>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        Christoph Hellwig <hch@....de>,
        David Woodhouse <dwmw2@...radead.org>,
        Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH] iommu/vt-d: Implement dma_[un]map_resource()

On Fri, Jan 18, 2019 at 05:05:59PM -0700, Logan Gunthorpe wrote:
> However, this doesn't create the IOVA entries necessary for addresses
> mapped this way to work when the IOMMU is enabled. Thus, when the
> IOMMU is enabled, drivers relying on dma_map_resource() will trigger
> DMAR errors. We see this when running ntb_transport with the IOMMU
> enabled, DMA, and switchtec hardware.

Which resources do you plan to map?  At least for PCIe P2P adding
an address translation seems wrong to me.

> 
> The implementation for intel_map_resource() is nearly identical to
> intel_map_page(), we just have to re-create __intel_map_single().
> dma_unmap_resource() uses intel_unmap_page() directly as the
> functions are identical.

Instead of having two tiny wrappers I'd just revert
964f2311a6862f1fbcc044d0828ad90030928b7f if we need to pass a real
physical address now.