Oof, that erratum; thanks for the heads up. I guess that means there should be some mechanism to replace (other uses of) sfence_vma_page with sfence_vma on effected chips? I think specifically for this case, though, it's fine: the ITLB may still fill with the old entry before this sfence.vma, but pmap_fault only changes A/D here. I suppose there could be an extra fault delivered from caching an A-clear PTE (if the load is done now by some very prognosticative speculation, say) despite that pmap_fault just set it, and I imagine the ITLB doesn't care about D at all. This extra fault will land us here again and cause another sfence.vma and even if the ITLB simultaneously refills the PTE about to be sfence.vma-ed, it will definitely see the A-set PTE from the last go around. That is, I don't think this makes anything worse.

Yes, this does look like it fixes the original panic I saw as well as my hand-written test. Thanks!

Thanks to @markj for the explanation; this is an incorrect fix.

Well, for whatever it's worth, the reproducer seems not to panic on amd64, which is a little surprising as I don't see any special handling for setting PG_M on !VPO_UNMANAGED, PG_RW, psind=1 pages in pmap_enter(), and I'd have thought the MI layers were doing the same thing on both.

Just the casts now, no function or structure type changes. This appears to pass muster locally.

Renamed macro as per mhorne's feedback

Incorporate feedback from @mhorne

Sorry, newbie learning way around arc. Seems it grabbed an unintended commit.

Slightly less code motion; tested using qemu "-append -s" on FreeBSD machine I'd forgotten about.

Revised in light of jrtc27's comments. Unfortunately, I lack a FreeBSD box to build and test this on (sorry, CheriBSD builds fine and I didn't think about our being lagged relative to upstream); perhaps someone who does would be so kind as to let me know if I've broken something?

Feedback from mhorne.

Yes, that's a fine "Submitted by".

More respose to markj feedback

Revised version as per markj's feedback

Now without D24523 included