What: /sys/devices/system/machinecheck/machinecheckX/tolerant
Contact: Borislav Petkov <bp@suse.de>
Date: Dec, 2021
Description:
Unused and obsolete after the advent of recoverable machine
checks (see last sentence below) and those are present since
2010 (Nehalem).
Original description:
The entries appear for each CPU, but they are truly shared
between all CPUs.
Tolerance level. When a machine check exception occurs for a
non corrected machine check the kernel can take different
actions.
Since machine check exceptions can happen any time it is
sometimes risky for the kernel to kill a process because it
defies normal kernel locking rules. The tolerance level
configures how hard the kernel tries to recover even at some
risk of deadlock. Higher tolerant values trade potentially
better uptime with the risk of a crash or even corruption
(for tolerant >= 3).
== ===========================================================
0 always panic on uncorrected errors, log corrected errors
1 panic or SIGBUS on uncorrected errors, log corrected errors
2 SIGBUS or log uncorrected errors, log corrected errors
3 never panic or SIGBUS, log all errors (for testing only)
== ===========================================================
Default: 1
Note this only makes a difference if the CPU allows recovery
from a machine check exception. Current x86 CPUs generally
do not.
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