[Skiboot] [PATCH v2 1/2] mbox: Harden against BMC daemon errors

[Nicholas Piggin]

On Fri, 23 Mar 2018 10:56:51 +1100
Cyril Bur <cyril.bur at au1.ibm.com> wrote:

> Bugs present in the BMC daemon mean that skiboot gets presented with
> mbox windows of size zero. These windows cannot be valid and skiboot
> already detects these conditions.
> 
> Currently skiboot warns quite strongly about the occurrence of these
> problems. The problem for skiboot is that it doesn't take any action.
> Initially I wanting to avoid putting policy like this into skiboot but
> since these bugs aren't going away and skiboot barfing is leading to
> lockups and ultimately the host going down something needs to be done.
> 
> I propose that when we detect the problem we fail the mbox call and punt
> the problem back up to Linux. I don't like it but at least it will cause
> errors to cascade and won't bring the host down. I'm not sure how Linux
> is supposed to detect this or what it can even do but this is better
> than a crash.
> 
> Diagnosing a failure to boot if skiboot its self fails to read flash may
> be marginally more difficult with this patch. This is because skiboot
> will now only print one warning about the zero sized window rather than
> continuously spitting it out.
> 
> Reported-by: Pridhiviraj Paidipeddi <ppaidipe at linux.vnet.ibm.com>
> Tested-by: Pridhiviraj Paidipeddi <ppaidipe at linux.vnet.ibm.com>
> Signed-off-by: Cyril Bur <cyril.bur at au1.ibm.com>

Reviewed-by: Nicholas Piggin <npiggin at gmail.com>