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[2.1 backport] Avoid save/restoring AMX registers to avoid a SPR erratum #15969

Merged
merged 1 commit into from
Apr 3, 2024
Merged

[2.1 backport] Avoid save/restoring AMX registers to avoid a SPR erratum #15969

merged 1 commit into from
Apr 3, 2024

Commits on Mar 6, 2024

  1. 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.

Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Rich Ercolani <[email protected]>
Closes openzfs#14989
Closes openzfs#15168

Signed-off-by: Rich Ercolani <[email protected]>
    @rincebrain
    rincebrain committed Mar 6, 2024
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