linux-kernel - Re: [PATCH] vmd: Stop overriding dma_map

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Date:   Tue, 27 Aug 2019 18:24:05 +0000
From:   "Derrick, Jonathan" <jonathan.derrick@...el.com>
To:     "hch@....de" <hch@....de>, "x86@...nel.org" <x86@...nel.org>
CC:     "joro@...tes.org" <joro@...tes.org>,
        "Busch, Keith" <keith.busch@...el.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "dwmw2@...radead.org" <dwmw2@...radead.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] vmd: Stop overriding dma_map_ops

On Mon, 2019-08-26 at 17:06 +0200, Christoph Hellwig wrote:
> With a little tweak to the intel-iommu code we should be able to work
> around the VMD mess for the requester IDs without having to create giant
> amounts of boilerplate DMA ops wrapping code.  The other advantage of
> this scheme is that we can respect the real DMA masks for the actual
> devices, and I bet it will only be a matter of time until we'll see the
> first DMA challeneged NVMe devices.
> 
> The only downside is that we can't offer vmd as a module given that
> intel-iommu calls into it.  But the driver only has about 700 lines
> of code, so this should not be a major issue.
If we're going to remove its ability to be a module, and given its
small size, could we make this default =y?

Otherwise we risk breaking platforms which have it enabled with OSVs
who miss enabling it


> 
> This also removes the leftover bits of the X86_DEV_DMA_OPS dma_map_ops
> registry.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
> 

lgtm otherwise

Reviewed-by: Jon Derrick <jonathan.derrick@...el.com>