x86: support sending non-fatal MCA messages to syslog

[jtl]

Summary

Currently, all machine-check errors are logged to the console. However, this can have performance implications which can turn a storm of correctable errors into disruptive events.

Provide an option to direct non-fatal messages to syslog. Note that we will always log to the console for fatal errors and errors directly printed from a hardware interrupt context.

Test Plan

Use the mechanism in D52942 to create artificial events for testing.

[jhb]

FreeBSD/sys/x86/x86/mca.c

305 ↗

(On Diff #32807)

I'm a bit leery of putting 1k on the stack. I have some old patches to use dedicated stacks for MC# (similar to what we do for NMI) which we might consider at some point and which would perhaps alleviate that worry.

[emaste]

ping

[jtl]

Updating to apply cleanly on top of D52946, which introduces the use of sbuf to gather the log message.

[markj]

sys/x86/x86/mca.c

776

IMO it's nicer to avoid breaking the line, that way it's easier to grep.

776

780

Maybe print the actual error number too?

[jtl]

incorporate review feedback; rebase on top of changes to D52946