[2.1 backport] Avoid save/restoring AMX registers to avoid a SPR erratum #15969
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Intel SPR erratum SPR4 says that if you trip into a vmexit while doing FPU save/restore, your AMX register state might misbehave... and by misbehave, I mean save all zeroes incorrectly, leading to explosions if you restore it. Since we're not using AMX for anything, the simple way to avoid this is to just not save/restore those when we do anything, since we're killing preemption of any sort across our save/restores. If we ever decide to use AMX, it's not clear that we have any way to mitigate this, on Linux...but I am not an expert. Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Rich Ercolani <rincebrain@gmail.com> Closes openzfs#14989 Closes openzfs#15168 Signed-off-by: Rich Ercolani <rincebrain@gmail.com>
behlendorf
approved these changes
Apr 3, 2024
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Motivation and Context
Someone hit #14989 on 2.1.x, and I noticed this hadn't ever ended up there.
I don't know if we're cutting a 2.1.16, but I figured I'd push it out in case someone needed it.
Description
See #15168
How Has This Been Tested?
Isn't that what CI is for?
Types of changes
Checklist:
Signed-off-by.