Re: [PATCH] swiotlb: ensure io_tlb_default_mem spinlock always initialised

[Ben Dooks]

On 11/07/2022 11:21, Christoph Hellwig wrote:
> 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.

Possibly, we had at least one driver which attempted to set a 32 bit
DMA mask which had to be removed as the DMA layer accepts this but
since there is no DMA32 memory the allocator then just fails.

I expect the above may need to be a separate discussion(s) of how to
default the DMA mask and how to stop the implicit acceptance of setting
a 32-bit DMA mask.
> > 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.