Messages in this thread | | | Date | Sun, 12 Jun 2011 13:30:07 +0300 | From | Avi Kivity <> | Subject | Re: [PATCH 07/10] MCE: replace mce.c use of TIF_MCE_NOTIFY with user_return_notifier |
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On 06/12/2011 01:24 PM, Borislav Petkov wrote: > On Sun, Jun 12, 2011 at 04:29:41AM -0400, Avi Kivity wrote: > > On 06/10/2011 12:35 AM, Luck, Tony wrote: > > > From: Tony Luck<tony.luck@intel.com> > > > > > > Ingo wrote: > > > > We already have a generic facility to do such things at > > > > return-to-userspace: _TIF_USER_RETURN_NOTIFY. > > > > > > This just a proof of concept patch ... before this can become > > > real the user-return-notifier code would have to be made NMI > > > safe (currently it uses hlist_add_head/hlist_del, which would > > > need to be changed to Ying's NMI-safe single threaded lists). > > > > You could use irq_work_queue() to push this into an irq context, which > > is user-return-notifier safe. > > Maybe I'm missing something but it looks like irq_work_queue() queues > work which is run in irq_work_run() with IRQs disabled. However, user > return notifiers are run after IRQs get enabled in entry_64.S. And we > want to run memory_failure() with IRQs enabled. > > More importantly, we want to be able to do the following: > > * run #MC handler which queues work > > * when returning to userspace, preempt and schedule that previously > queued work _before_ the process that caused the MCE gets to execute.
Yes.
> Imagine this scenario: > > Your userspace process causes a data cache read error due to either > alpha particles or maybe because the DRAM device containing the process > page is faulty and generates ECC errors which the ECC code cannot > correct, i.e. an uncorrectable error we definitely want to handle; IOW > Action Required MCE. > > Now, if you get lucky and this page is mapped only by the process that > caused the MCE, you could unmap it, mark it PageReserved and cause the > process to refault. But in order to do that, you want to execute the > memory_failure() handler _before_ you schedule the process again. > > In the instruction cache read error case, you don't have processor > context to return to (or you're being too conservative and don't want to > risk it) so you kill the process, which is pretty easy to do. > > Does that make a bit more sense? Tony? >
You're missing the flow. The MCE handler calls irq_work_queue(), which schedules a user return notifier, which does any needed processing in task context.
-- error compiling committee.c: too many arguments to function
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