Re: [PATCH] Revert "ALSA: memalloc: Workaround for Xen PV"

[Takashi Iwai <tiwai@suse.de>]

On Thu, 12 Sep 2024 11:56:21 +0200,
Christoph Hellwig wrote:
> 
> On Sat, Sep 07, 2024 at 11:38:50AM +0100, Andrew Cooper wrote:
> > Individual subsystems ought not to know or care about XENPV; it's a
> > layering violation.
> 
> Agreed.
> 
> > If the main APIs don't behave properly, then it probably means we've got
> > a bug at a lower level (e.g. Xen SWIOTLB is a constant source of fun)
> > which is probably affecting other subsystems too.
> > 
> > I think we need to re-analyse the original bug.  Right now, the
> > behaviour resulting from 53466ebde is worse than what it was trying to fix.
> 
> 53466ebde looks bogus to me, and the commit message doesn't even
> try to explain what bad behavior it works around.  I'd also like to
> state once again that if you think something is broken about dma
> allocation or mapping helpers please Cc me and the iommu list.
> 
> Most of the time it's actually the drivers doing something invalid, but
> sometimes it is a core dma layer bug or something that needs a proper
> API.
> 
> Also while looking at the above commit I noticed the broken fallback
> code in snd_dma_noncontig_alloc - get_dma_ops is not for driver use,
> and starting with the code queued up for 6.12 will also return NULL
> when using dma-iommu for example.

Yes, all those are really ugly hacks and have been already removed for
6.12.  Let's hope everything works as expected with it.


thanks,

Takashi