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

From: Christoph Hellwig
Date: Mon Jul 11 2022 - 07:17:33 EST


On Mon, Jul 11, 2022 at 11:24:51AM +0100, Ben Dooks wrote:
> 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.

No. Linux simply assumes you can do 32-bit DMA and this won't
change. So we'll need to fix your platform to support swiotlb
eventually.