linux-kernel - Re: [PATCH] swiotlb: ensure io_tlb_default

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Date:   Mon, 11 Jul 2022 12:21:34 +0200
From:   Christoph Hellwig <hch@....de>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Ben Dooks <ben.dooks@...ive.com>, linux-kernel@...r.kernel.org,
        iommu@...ts.linux.dev, iommu@...ts.linux-foundation.org,
        Christoph Hellwig <hch@....de>,
        Sudip Mukherjee <sudip.mukherjee@...ive.com>,
        Jude Onyenegecha <jude.onyenegecha@...ive.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [PATCH] swiotlb: ensure io_tlb_default_mem spinlock always
 initialised

On Mon, Jul 11, 2022 at 11:07:17AM +0100, Robin Murphy wrote:
> If none of your peripherals should need SWIOTLB, then the fact that
> you're ending up in swiotlb_map() at all is a clear sign that
> something's wrong. Most likely someone's forgotten to set their DMA
> masks correctly.

Yes.

>
> However, by inspection it seems we do have a bug here as well, for which
> the correct fix should be as below. The fireworks you're *supposed* to
> get in that situation are considerably louder and more obvious than a
> DEBUG_SPINLOCK complaint ;)

This looks sensible, I'll pick it up.