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Avoid save/restoring AMX registers to avoid a SPR erratum
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. Fixes: openzfs#14989 Signed-off-by: Rich Ercolani <[email protected]>
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