Re: Hardware Error Kernel Mini-Summit

[Ingo Molnar <mingo@elte.hu>]

* Borislav Petkov <bp@amd64.org> wrote:

> Well, we have a trace_mce_record tracepoint in the 
> mcheck code which calls all the necessary callbacks when 
> an mcheck occurs. For the time being, the idea is to use 
> the mce.c ring buffer for early mchecks and copy them to 
> the regular ftrace per-cpu buffer after the last has 
> been initialized. Later, we could switch to a another 
> early bootmem buffer if there's need to.

The end result would be even simpler by one more step: 
with persistent events we just use them and dont need the 
mce.c ringbuffer at all. (getting rid of that complication 
is one of the code cleanliness benefits i see in this move 
as a x86 maintainer - beyond the obvious generalization 
and unification benefits.)

> Also, we want to have a userspace daemon that reads out 
> the mces from the trace buffer and does further 
> processing like thresholding etc in userspace.
> 
> Concerning critical errors, there we bypass the perf 
> subsystem and execute the smallest amount of code 
> possible while trying to shutdown gracefully if the 
> error type allows that.

Yeah. Each perf_event can have arbitrary callbacks with 
add-on (or critical) functionality. We would activate the 
event(s) during bootup and it would do its thing from that 
point on: critical functionality gets a direct path via 
the callback, and every other event that survives goes via 
the regular perf output channels, to one (or more) 
consumers/subscribers of these events.

	Ingo