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

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Message-ID: <3e715fb9-7a0d-046a-c32c-bc6afbecf55e@arm.com>
Date:   Tue, 22 Mar 2022 09:53:29 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Christoph Hellwig <hch@....de>
Cc:     michael.jamet@...el.com, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, YehezkelShB@...il.com,
        iommu@...ts.linux-foundation.org, mario.limonciello@....com,
        andreas.noever@...il.com, mika.westerberg@...ux.intel.com
Subject: Re: [PATCH v2 1/2] iommu: Add capability for pre-boot DMA protection

On 2022-03-22 09:14, Christoph Hellwig wrote:
> 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:

Well, you were the first to say it should be abstracted[1], and since my 
initial thought that it could be hidden completely didn't pan out, I 
felt I should give you credit for being right all along :)

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

Thanks!

Robin.

[1] https://lore.kernel.org/linux-iommu/YjDDUUeZ%2FdvUZoDN@infradead.org/