linux-kernel - Re: [PATCH v2 1/2] iommu: Add capability for pre-boot DMA protection

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Date:   Tue, 22 Mar 2022 10:14:32 +0100
From:   Christoph Hellwig <hch@....de>
To:     Robin Murphy <robin.murphy@....com>
Cc:     joro@...tes.org, baolu.lu@...ux.intel.com,
        andreas.noever@...il.com, michael.jamet@...el.com,
        mika.westerberg@...ux.intel.com, YehezkelShB@...il.com,
        iommu@...ts.linux-foundation.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, mario.limonciello@....com, hch@....de
Subject: Re: [PATCH v2 1/2] iommu: Add capability for pre-boot DMA
 protection

On Fri, Mar 18, 2022 at 05:42:57PM +0000, Robin Murphy wrote:
> VT-d's dmar_platform_optin() actually represents a combination of
> properties fairly well standardised by Microsoft as "Pre-boot DMA
> Protection" and "Kernel DMA Protection"[1]. As such, we can provide
> interested consumers with an abstracted capability rather than
> driver-specific interfaces that won't scale. We name it for the former
> aspect since that's what external callers are most likely to be
> interested in; the latter is for the IOMMU layer to handle itself.
> 
> Also use this as an opportunity to draw a line in the sand and add a
> new interface so as not to introduce any more callers of iommu_capable()
> which I also want to get rid of. For now it's a quick'n'dirty wrapper
> function, but will evolve to subsume the internal interface in future.
> 
> [1] https://docs.microsoft.com/en-us/windows-hardware/design/device-experiences/oem-kernel-dma-protection
> 
> Suggested-by: Christoph Hellwig <hch@....de>
> Signed-off-by: Robin Murphy <robin.murphy@....com>

I can't really think of a way in which I suggested this, but it does
looks like a good interface:

Reviewed-by: Christoph Hellwig <hch@....de>