On Fri, Jan 26, 2024, Xiong Zhang wrote:
> From: Xiong Zhang <xiong.y.zhang@xxxxxxxxx>
>
> The perf event for NMI watchdog is per cpu pinned system wide event,
> if such event doesn't have exclude_guest flag, it will be put into
> error state once guest with passthrough PMU starts, this breaks
> NMI watchdog function totally.
>
> This commit adds exclude_guest flag for this perf event, so this perf
> event is stopped during VM running, but it will continue working after
> VM exit. In this way the NMI watchdog can not detect hardlockups during
> VM running, it still breaks NMI watchdog function a bit. But host perf
> event must be stopped during VM with passthrough PMU running, current
> no other reliable method can be used to replace perf event for NMI
> watchdog.
As mentioned in the cover letter, I think this is backwards, and mediated PMU
support should be disallowed if kernel-priority things like the watchdog are in
use.
Doubly so because this patch affects _everything_, not just systems with VMs
that have a mediated PMU.
> Signed-off-by: Xiong Zhang <xiong.y.zhang@xxxxxxxxx>
> Signed-off-by: Mingwei Zhang <mizhang@xxxxxxxxxx>
> ---
> kernel/watchdog_perf.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/kernel/watchdog_perf.c b/kernel/watchdog_perf.c
> index 8ea00c4a24b2..c8ba656ff674 100644
> --- a/kernel/watchdog_perf.c
> +++ b/kernel/watchdog_perf.c
> @@ -88,6 +88,7 @@ static struct perf_event_attr wd_hw_attr = {
> .size = sizeof(struct perf_event_attr),
> .pinned = 1,
> .disabled = 1,
> + .exclude_guest = 1,
> };
>
> /* Callback function for perf event subsystem */
> --
> 2.34.1
>
