Messages in this thread | | | From | Andy Lutomirski <> | Date | Wed, 12 Nov 2014 19:03:21 -0800 | Subject | Re: [RFC PATCH] x86, entry: Switch stacks on a paranoid entry from userspace |
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On Wed, Nov 12, 2014 at 4:31 PM, Luck, Tony <tony.luck@intel.com> wrote: >> v2's not going to make a difference unless you're using uprobes at the >> same time. > > Not (knowingly) using uprobes. System is installed with a RHEL7 userspace ... but is essentially > idle except for my test program. > >> In the interest of my sanity, can you add something like >> BUG_ON(!user_mode_vm(regs)) or the mce_panic equivalent before calling >> memory_failure? > > I don't think that can possibly trip - we can only end up with a recoverable error from > a user mode access. But I'll see about adding it anyway > >> What happens if there's a shared bank but the actual offender has a >> higher order than the cpu that finds the error? > > This test case injects a memory error which is logged in bank1. This bank is shared by the > two hyperthreads that are on the same core. The mce_severity() function distinguishes > which is the active thread and which the innocent bystander by looking at MCG_STATUS. > In the active thread MCG_STATUS.EIPV is 1, in the bystander it is 0. The returned severity > is MCE_AR_SEVERITY for the thread that hit the error, MCE_KEEP_SEVERITY for the bystander. > So it doesn't matter which thread has the lower order and sees it first. > >> Is this something I can try under KVM? > > I don't know if KVM has a way to simulate a machine check event.
printk seems to work just fine in do_machine_check. Any chance you can instrument, for each cpu, all entries to do_machine_check, all calls to do_machine_check, all returns, and everything that tries to do memory_failure?
Also, shouldn't there be a local_irq_enable before memory_failure and a local_irq_disable after it? It wouldn't surprise me if you've deadlocked somewhere. Lockdep could also have something interesting to say.
(Although I'm a bit confused. A deadlock in memory_failure shouldn't cause the particular failure mode you're seeing, since a new #MC should still be deliverable. Is it possible that we really need an IRET to unmask NMIs? This seems unlikely.)
--Andy
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