Re: [PATCH] x86/nmi: Make external NMI injection reliably crash the host

[Don Slutz <dslutz@verizon.com>]

On 08/26/14 12:51, Andrew Cooper wrote:
> On 26/08/14 17:06, Don Slutz wrote:
>> On 08/26/14 06:10, Ross Lagerwall wrote:
>>> Change the watchdog handler to only "tick" if the corresponding perf
>>> counter has overflowed; otherwise, return false from the NMI handler to
>>> indicate that the NMI is not a watchdog tick and let the other handlers
>>> handle it.  This allows externally injected NMIs to reliably crash the
>>> host rather than be swallowed by the watchdog handler.
>> If a crash kernel has been setup via kexec, does this change to
>> "crash host" ends up jumping into the crash kernel?
>>
>>      -Don Slutz
> No - this has no change of behaviour as to how Xen proceeds after it has
> decided to panic().
>
> It does however change whether Xen decided to panic, depending on
> whether the NMI was a result of the watchdog, or some otherwise
> unidentified NMI.
>
> Basically, without this change, the "inject fatal NMI" option in most
> IPMI controllers doesn't work in combination with running the Xen
> watchdog.  Only certain HP systems appear to set the IOCK bit in the
> system control port B when injecting an NMI.  All other systems just
> send an NMI with no change to the control ports, which get eaten by the
> watchdog logic.
>
> This patch changes the watchdog logic to only consider an NMI as a
> watchdog tick if the perf counter confirms that it injected the NMI.

Well, that is useful information.  Looks like I was not clear.  I am reading

> as to how Xen proceeds after it has

 > decided to panic().


As a yes, but you start with a no.  And I am getting "crash host" to 
mean "calls panic()".

    -Don Slutz

> ~Andrew