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Configurable sysfs parameters for the x86-64 machine check code.
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Machine checks report internal hardware error conditions detected
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by the CPU. Uncorrected errors typically cause a machine check
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(often with panic), corrected ones cause a machine check log entry.
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Machine checks are organized in banks (normally associated with
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a hardware subsystem) and subevents in a bank. The exact meaning
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of the banks and subevent is CPU specific.
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mcelog knows how to decode them.
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When you see the "Machine check errors logged" message in the system
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log then mcelog should run to collect and decode machine check entries
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from /dev/mcelog. Normally mcelog should be run regularly from a cronjob.
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Each CPU has a directory in /sys/devices/system/machinecheck/machinecheckN
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(N = CPU number)
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The directory contains some configurable entries:
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Entries:
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bankNctl
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(N bank number)
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64bit Hex bitmask enabling/disabling specific subevents for bank N
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When a bit in the bitmask is zero then the respective
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subevent will not be reported.
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By default all events are enabled.
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Note that BIOS maintain another mask to disable specific events
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per bank. This is not visible here
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The following entries appear for each CPU, but they are truly shared
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between all CPUs.
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check_interval
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How often to poll for corrected machine check errors, in seconds
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(Note output is hexadecimal). Default 5 minutes. When the poller
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finds MCEs it triggers an exponential speedup (poll more often) on
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the polling interval. When the poller stops finding MCEs, it
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triggers an exponential backoff (poll less often) on the polling
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interval. The check_interval variable is both the initial and
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maximum polling interval. 0 means no polling for corrected machine
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check errors (but some corrected errors might be still reported
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in other ways)
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tolerant
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Tolerance level. When a machine check exception occurs for a non
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corrected machine check the kernel can take different actions.
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Since machine check exceptions can happen any time it is sometimes
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risky for the kernel to kill a process because it defies
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normal kernel locking rules. The tolerance level configures
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how hard the kernel tries to recover even at some risk of
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deadlock. Higher tolerant values trade potentially better uptime
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with the risk of a crash or even corruption (for tolerant >= 3).
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0: always panic on uncorrected errors, log corrected errors
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1: panic or SIGBUS on uncorrected errors, log corrected errors
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2: SIGBUS or log uncorrected errors, log corrected errors
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3: never panic or SIGBUS, log all errors (for testing only)
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Default: 1
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Note this only makes a difference if the CPU allows recovery
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from a machine check exception. Current x86 CPUs generally do not.
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trigger
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Program to run when a machine check event is detected.
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This is an alternative to running mcelog regularly from cron
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and allows to detect events faster.
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monarch_timeout
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How long to wait for the other CPUs to machine check too on a
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exception. 0 to disable waiting for other CPUs.
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Unit: us
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TBD document entries for AMD threshold interrupt configuration
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For more details about the x86 machine check architecture
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see the Intel and AMD architecture manuals from their developer websites.
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For more details about the architecture see
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see http://one.firstfloor.org/~andi/mce.pdf
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