regression with SG DMA buf allocations and IOMMU in low-mem

[Kai Vehmanen]

Hi,

On Fri, 4 Nov 2022, Takashi Iwai wrote:

> On Fri, 04 Nov 2022 16:42:29 +0100, Kai Vehmanen wrote:
> > I think an explicit error would be best. The problem now is that the 
> > driver will think the allocation (and mapping to device) is fine and 
> > proceeds to program the hardware to use the address. This will then create 
> > an IOMMU fault down the line that is not so straighforward to recover from 
> > (worst case is that a full device level reset needs to be done). And given 
> > driver doesn't know it got a faulty mapping, it's hard to make the 
> > decision why the fault happened.
> 
> OK, then what I posted in another mail (it went to nirvana) might
> work.  Attached below again.

thanks! Let me put this through testing and get back to you next 
week. We'll also debug a bit more what exactly goes on that leads to 
dma_alloc_noncontiguous failing.

Br, Kai