Re: [PATCH v15 06/12] swiotlb: Use is_swiotlb_force_bounce for swiotlb data bouncing

On Tue, Jul 06, 2021 at 04:05:13PM +0200, Christoph Hellwig wrote:

On Tue, Jul 06, 2021 at 03:01:04PM +0100, Robin Murphy wrote:

quoted

FWIW I was pondering the question of whether to do something along those 
lines or just scrap the default assignment entirely, so since I hadn't got 
round to saying that I've gone ahead and hacked up the alternative 
(similarly untested) for comparison :)

TBH I'm still not sure which one I prefer...

Claire did implement something like your suggestion originally, but
I don't really like it as it doesn't scale for adding multiple global
pools, e.g. for the 64-bit addressable one for the various encrypted
secure guest schemes.

Couple of things:
 - I am not pushing to Linus the Claire's patchset until we have a
   resolution on this. I hope you all agree that is a sensible way
   forward as much as I hate doing that.

 - I like Robin's fix as it is simplest looking. Would love to see if it
   does fix the problem.

 - Christopher - we can always add multiple pools as the next milestone
   and just focus on this feature getting tested extensively during this
   release.

 - Would it be worth (for future or maybe in another tiny fix) to also add
   a printk in swiotlb when we de-allocate the buffer so when someone looks
   through the `dmesg` it becomes much easier to diagnose issues?