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Re: 4.4-rc5 Setting trap flag inside nmi handler results in HARD LOCKUP

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On 12/16/15, Jeff Merkey <linux.mdb@gmail.com> wrote:
> Setting the (trap flag | resume flag) inside of an nmi handler results
> in a hard lockup while setting the resume flag works fine.
>
> The watchdog detector fails to detect the lockup.  I am currently
> examining the trap gate and interrupt gate setup on Linux and if
> anyone has any ideas it would be nice to be able to debug and step
> through the nmi handlers.  I got breakpoints to work.  I noticed
> kgdb/kdb just punts here and refuses to allow someone to step inside
> an nmi handler.
>
> There is no reason Linux should not allow this to work since windows
> does and every other OS out there.  I have seen this across some rex64
> sysret calls as well this lockup behavior.
>
> Anyone who is an intel expert with any clues would love some input if
> you know about this problem.
>
> Jeff
>

More info.  Linux is getting a trap and it looks like the IDT is
getting swapped when it gets it -- POW - Dead Linux.

Damn ...  Well, it will be long night and lots of builds ...

Jeff
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Thread

4.4-rc5 Setting trap flag inside nmi handler results in HARD LOCKUP Jeff Merkey <linux.mdb@gmail.com> - 2015-12-16 19:20 +0100
  Re: 4.4-rc5 Setting trap flag inside nmi handler results in HARD LOCKUP Jeff Merkey <linux.mdb@gmail.com> - 2015-12-16 19:50 +0100
    Re: 4.4-rc5 Setting trap flag inside nmi handler results in HARD LOCKUP Jeff Merkey <linux.mdb@gmail.com> - 2015-12-16 22:50 +0100
    Re: 4.4-rc5 Setting trap flag inside nmi handler results in HARD LOCKUP Jeff Merkey <linux.mdb@gmail.com> - 2015-12-16 23:10 +0100
  Re: 4.4-rc5 Setting trap flag inside nmi handler results in HARD LOCKUP Jeff Merkey <linux.mdb@gmail.com> - 2015-12-17 08:30 +0100

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