Re: [PATCH v3] xen: add support for automatic debug key actions in case of crash

[Jan Beulich <jbeulich@xxxxxxxx>]

On 09.12.2020 13:11, Julien Grall wrote:
> On 26/11/2020 11:20, Jan Beulich wrote:
>> On 26.11.2020 09:03, Juergen Gross wrote:
>>> When the host crashes it would sometimes be nice to have additional
>>> debug data available which could be produced via debug keys, but
>>> halting the server for manual intervention might be impossible due to
>>> the need to reboot/kexec rather sooner than later.
>>>
>>> Add support for automatic debug key actions in case of crashes which
>>> can be activated via boot- or runtime-parameter.
>>>
>>> Depending on the type of crash the desired data might be different, so
>>> support different settings for the possible types of crashes.
>>>
>>> The parameter is "crash-debug" with the following syntax:
>>>
>>>    crash-debug-<type>=<string>
>>>
>>> with <type> being one of:
>>>
>>>    panic, hwdom, watchdog, kexeccmd, debugkey
>>>
>>> and <string> a sequence of debug key characters with '+' having the
>>> special semantics of a 10 millisecond pause.
>>>
>>> So "crash-debug-watchdog=0+0qr" would result in special output in case
>>> of watchdog triggered crash (dom0 state, 10 ms pause, dom0 state,
>>> domain info, run queues).
>>>
>>> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
>>> ---
>>> V2:
>>> - switched special character '.' to '+' (Jan Beulich)
>>> - 10 ms instead of 1 s pause (Jan Beulich)
>>> - added more text to the boot parameter description (Jan Beulich)
>>>
>>> V3:
>>> - added const (Jan Beulich)
>>> - thorough test of crash reason parameter (Jan Beulich)
>>> - kexeccmd case should depend on CONFIG_KEXEC (Jan Beulich)
>>> - added dummy get_irq_regs() helper on Arm
>>>
>>> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
>>
>> Except for the Arm aspect, where I'm not sure using
>> guest_cpu_user_regs() is correct in all cases,
> 
> I am not entirely sure to understand what get_irq_regs() is supposed to 
> returned on x86. Is it the registers saved from the most recent exception?

An interrupt (not an exception) sets the underlying per-CPU
variable, such that interested parties will know the real
context is not guest or "normal" Xen code, but an IRQ.

Jan