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

Hi Will and Robin,

On 7/6/2021 10:06 AM, Will Deacon wrote:
On Tue, Jul 06, 2021 at 04:39:11PM +0100, Robin Murphy wrote:
On 2021-07-06 15:05, Christoph Hellwig wrote:
On Tue, Jul 06, 2021 at 03:01:04PM +0100, Robin Murphy wrote:
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.

Ah yes, that had slipped my mind, and it's a fair point indeed. Since we're
not concerned with a minimal fix for backports anyway I'm more than happy to
focus on Will's approach. Another thing is that that looks to take us a
quiet step closer to the possibility of dynamically resizing a SWIOTLB pool,
which is something that some of the hypervisor protection schemes looking to
build on top of this series may want to explore at some point.

Ok, I'll split that nasty diff I posted up into a reviewable series and we
can take it from there.

For what it's worth, I attempted to boot Will's diff on top of Konrad's devel/for-linus-5.14 and it did not work; in fact, I got no output on my monitor period, even with earlyprintk=, and I do not think this machine has a serial console.

Robin's fix does work, it survived ten reboots with no issues getting to X and I do not see the KASAN and slub debug messages anymore but I understand that this is not the preferred solution it seems (although Konrad did want to know if it works).

I am happy to test any further patches or follow ups as needed, just keep me on CC.




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