Avoid save/restoring AMX registers to avoid a SPR erratum #15168
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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. Fixes: openzfs#14989 Signed-off-by: Rich Ercolani <[email protected]>
behlendorf
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Aug 26, 2023
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Aug 26, 2023
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
behlendorf
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Aug 27, 2023
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 #14989 Closes #15168
lundman
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Dec 12, 2023
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
rincebrain
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Mar 6, 2024
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]>
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behlendorf
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Apr 3, 2024
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 #14989 Closes #15168 Signed-off-by: Rich Ercolani <[email protected]>
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Motivation and Context
#14989
Description
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 (apparently) 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.
How Has This Been Tested?
Reporter of #14989 has been running the same workaround for weeks without breaking.
Types of changes
Checklist:
Signed-off-by.