[Bug 293382] Dead lock and kernel crash around closefp_impl

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=293382

--- Comment #85 from Kristofer Peterson <kris@tranception.com> ---
(In reply to Kyle Evans from comment #79)

It seems hardware support is a bit more nuanced than just Zen4/Zen5.
I've only seen this on EPYC 8xxx and 9xxx CPUs; I have other boxes with Ryzen 9
CPUs (i.e. 7950X) which I have never been able to reproduce this problem on.
The Ryzen 7950X is Zen4 however I can see that bit 3 of CPUID Fn8000_0008_EBX
on that box is cleared (i.e. no INVLPGB support).

I gather from your most recent post that the AMD hardware you have can
reproduce this problem so this is perhaps unsurprising, however I think this
safely narrows the affected popoulation down from "big EPYC CPU with a lot of
RAM".

One time I tried a relatively weeny AMD EPYC 8024P box with only eight cores
but I did not see this issue - it is the runt of the 8xxx series so perhaps AMD
did not deign to bestow it with INVLPGB logic (much like the 7950X).

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