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4.4-rc5 Setting hardware breakpoint in int_ret_from_sys_call causes triple fault/reboot

From Jeff Merkey <linux.mdb@gmail.com>
Newsgroups linux.kernel
Subject 4.4-rc5 Setting hardware breakpoint in int_ret_from_sys_call causes triple fault/reboot
Date 2015-12-17 00:20 +0100
Message-ID <qGtwt-8ei-1@gated-at.bofh.it> (permalink)
Organization linux.* mail to news gateway

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Setting a hardware breakpoint at the

rex64 sysret

instruction at the end of int_ret_from_sys_call causes the system to
triple fault
and reboot when the breakpoint is triggered.  Appears to be related
the same problem
as the lockup.

This function can be stepped over and traced through with the TRAP
FLAG set so long as a hardware breakpoint is set somewhere in the
function.  Otherwise upon exist the system hard hangs.  If you break
exactly on that instruction -- reboot.   If you break a few
instructions before it and single step through the call it works.  If
you step through the call with no breakpoint the system hard hangs.
Same behavior as when you try to step from inside an nmi handler.
Looks related.

Caused somewhere in the way exception handlers are coded for sure.
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Thread

4.4-rc5 Setting hardware breakpoint in int_ret_from_sys_call causes  triple fault/reboot Jeff Merkey <linux.mdb@gmail.com> - 2015-12-17 00:20 +0100
  Re: 4.4-rc5 Setting hardware breakpoint in int_ret_from_sys_call  causes triple fault/reboot Andy Lutomirski <luto@amacapital.net> - 2015-12-17 01:10 +0100
    Re: 4.4-rc5 Setting hardware breakpoint in int_ret_from_sys_call  causes triple fault/reboot Jeff Merkey <linux.mdb@gmail.com> - 2015-12-17 01:40 +0100
      Re: 4.4-rc5 Setting hardware breakpoint in int_ret_from_sys_call  causes triple fault/reboot Andy Lutomirski <luto@amacapital.net> - 2015-12-17 01:40 +0100
        Re: 4.4-rc5 Setting hardware breakpoint in int_ret_from_sys_call  causes triple fault/reboot Jeff Merkey <linux.mdb@gmail.com> - 2015-12-17 01:50 +0100
          Re: 4.4-rc5 Setting hardware breakpoint in int_ret_from_sys_call  causes triple fault/reboot Jeff Merkey <linux.mdb@gmail.com> - 2015-12-17 09:40 +0100
            Re: 4.4-rc5 Setting hardware breakpoint in int_ret_from_sys_call  causes triple fault/reboot Jeff Merkey <linux.mdb@gmail.com> - 2015-12-17 20:00 +0100
      Re: 4.4-rc5 Setting hardware breakpoint in int_ret_from_sys_call  causes triple fault/reboot Jeff Merkey <linux.mdb@gmail.com> - 2015-12-17 01:40 +0100

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