Messages in this thread | | | From | Andy Lutomirski <> | Date | Wed, 21 May 2014 15:13:16 -0700 | Subject | Re: [RFC] x86_64: A real proposal for iret-less return to kernel |
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On Wed, May 21, 2014 at 3:01 PM, Luck, Tony <tony.luck@intel.com> wrote: >> But sending signals from #MC context is definitely a bad idea. I think >> we had addressed this with irq_work at some point but my memory is very >> hazy. > > We added code for recoverable errors to get out of the MC context > before trying to lookup the page and send the signal. Bottom of > do_machine_check(): > > if (cfg->tolerant < 3) { > if (no_way_out) > mce_panic("Fatal machine check on current CPU", &m, msg); > if (worst == MCE_AR_SEVERITY) { > /* schedule action before return to userland */ > mce_save_info(m.addr, m.mcgstatus & MCG_STATUS_RIPV); > set_thread_flag(TIF_MCE_NOTIFY); > } else if (kill_it) { > force_sig(SIGBUS, current); > } > } > > That TIF_MCE_NOTIFY prevents the return to user mode, and we end up in mce_notify_process().
Why is this necessary?
If the MCE hit kernel code, then we're going to die anyway. If the MCE hit user code, then we should be in a completely sensible context and we can just send the signal.
--Andy
> > The "force_sig()" there is legacy code - and perhaps should just move off to mce_notify_process() > too (need to save "worst" so it will know what to do). > > -Tony
-- Andy Lutomirski AMA Capital Management, LLC
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