Messages in this thread | | | From | Andy Lutomirski <> | Date | Wed, 12 Nov 2014 17:34:08 -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.
With mce-inject and this input:
CPU 1 BANK 0 STATUS uc s ar val en 0x0134 MCGSTATUS mcip eipv ADDR 4096 MISC 0 IN_PROC EXCP
I blow up because mce-inject doesn't have a credible emulation of process context (i.e. IN_PROC doesn't work).
--Andy
> > -Tony
-- Andy Lutomirski AMA Capital Management, LLC
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