Re: [PATCH 0/4] hw: make TCO watchdog actually work by default for Q35

[Michael S. Tsirkin]

On Mon, Oct 31, 2022 at 01:19:30PM +0000, Daniel P. Berrangé wrote:
> The TCO watchdog is unconditionally integrated into the Q35 machine
> type by default, but at the same time is unconditionally disabled
> from firing by a host config option that overrides guest OS attempts
> to enable it. People have to know to set a magic -global to make
> it non-broken
> 
> IOW we're exposing a broken watchdog by default to all Q35 machines,
> but which to the guest OS & its apps looks fully functional :-(
> 
> This behaviour was set in response to feedback from Michael:
> 
>   https://lists.gnu.org/archive/html/qemu-devel/2015-06/msg07128.html
> 
>     "I think sample high is a safer default."
> 
> but as explained in the commit message in the last patch, I think the
> watchdog defaults were already safe without that pin strap setting.
> The guest OS needs to take explicit action to clear the guest visible
> 'no reboot' flag, and so we don't need a second guest hidden 'no reboot'
> flag to override that choice IMHO. Am I missing something ?
> 
> NB, I'm toggling this for 7.2 machine type since that's the current
> git latest machine. Since this has already been "broken" for 7 years
> though, I am ambivalent about whether we try todo this for 7.2, vs
> just wait until the 8.0 machine types arrive.


So I expect v2 with minor issues fixed and hopefully a
fixed property (we can debate removing it down the road
if we want).


> Daniel P. Berrangé (4):
>   hw/acpi: add trace events for TCO watchdog register access
>   hw/isa: add trace events for ICH9 LPC chip config access
>   hw/watchdog: add trace events for watchdog action handling
>   hw/isa: enable TCO watchdog reboot pin strap by default
> 
>  hw/acpi/tco.c            | 41 +++++++++++++++++++++++++++-------------
>  hw/acpi/trace-events     |  2 ++
>  hw/i386/pc.c             |  4 +++-
>  hw/isa/lpc_ich9.c        |  5 ++++-
>  hw/isa/trace-events      |  4 ++++
>  hw/watchdog/trace-events |  4 ++++
>  hw/watchdog/watchdog.c   |  4 ++++
>  tests/qtest/tco-test.c   |  2 +-
>  8 files changed, 50 insertions(+), 16 deletions(-)
> 
> -- 
> 2.37.3