WSL2-Linux-Kernel/Documentation/watchdog/hpwdt.txt

Last reviewed: 05/20/2016

                     HPE iLO NMI Watchdog Driver
              NMI sourcing for iLO based ProLiant Servers
                     Documentation and Driver by
                         Thomas Mingarelli

 The HPE iLO NMI Watchdog driver is a kernel module that provides basic
 watchdog functionality and the added benefit of NMI sourcing. Both the
 watchdog functionality and the NMI sourcing capability need to be enabled
 by the user. Remember that the two modes are not dependent on one another.
 A user can have the NMI sourcing without the watchdog timer and vice-versa.
 All references to iLO in this document imply it also works on iLO2 and all
 subsequent generations.

 Watchdog functionality is enabled like any other common watchdog driver. That
 is, an application needs to be started that kicks off the watchdog timer. A
 basic application exists in tools/testing/selftests/watchdog/ named
 watchdog-test.c. Simply compile the C file and kick it off. If the system
 gets into a bad state and hangs, the HPE ProLiant iLO timer register will
 not be updated in a timely fashion and a hardware system reset (also known as
 an Automatic Server Recovery (ASR)) event will occur.

 The hpwdt driver also has three (3) module parameters. They are the following:

 soft_margin - allows the user to set the watchdog timer value.
               Default value is 30 seconds.
 allow_kdump - allows the user to save off a kernel dump image after an NMI.
               Default value is 1/ON
 nowayout    - basic watchdog parameter that does not allow the timer to
               be restarted or an impending ASR to be escaped.
               Default value is set when compiling the kernel. If it is set
               to "Y", then there is no way of disabling the watchdog once
               it has been started.

 NOTE: More information about watchdog drivers in general, including the ioctl
       interface to /dev/watchdog can be found in
       Documentation/watchdog/watchdog-api.txt and Documentation/IPMI.txt.

 The NMI sourcing capability is disabled by default due to the inability to
 distinguish between "NMI Watchdog Ticks" and "HW generated NMI events" in the
 Linux kernel. What this means is that the hpwdt nmi handler code is called
 each time the NMI signal fires off. This could amount to several thousands of
 NMIs in a matter of seconds. If a user sees the Linux kernel's "dazed and
 confused" message in the logs or if the system gets into a hung state, then
 the hpwdt driver can be reloaded.

 1. If the kernel has not been booted with nmi_watchdog turned off then
    edit and place the nmi_watchdog=0 at the end of the currently booting
    kernel line. Depending on your Linux distribution and platform setup:
    For non-UEFI systems
       /boot/grub/grub.conf   or
       /boot/grub/menu.lst
    For UEFI systems
      /boot/efi/EFI/distroname/grub.conf   or
      /boot/efi/efi/distroname/elilo.conf
 2. reboot the sever
 3. Once the system comes up perform a modprobe -r hpwdt
 4. modprobe /lib/modules/`uname -r`/kernel/drivers/watchdog/hpwdt.ko

 Now, the hpwdt can successfully receive and source the NMI and provide a log
 message that details the reason for the NMI (as determined by the HPE BIOS).

 Below is a list of NMIs the HPE BIOS understands along with the associated
 code (reason):

	No source found                00h

	Uncorrectable Memory Error     01h

	ASR NMI                        1Bh

	PCI Parity Error               20h

	NMI Button Press               27h

	SB_BUS_NMI                     28h

	ILO Doorbell NMI               29h

	ILO IOP NMI                    2Ah

	ILO Watchdog NMI               2Bh

	Proc Throt NMI                 2Ch

	Front Side Bus NMI             2Dh

	PCI Express Error              2Fh

	DMA controller NMI             30h

	Hypertransport/CSI Error       31h



 -- Tom Mingarelli