From: Tianyu Lan <Tianyu.Lan@xxxxxxxxxxxxx> Sent: Monday, March 23, 2020 6:09 AM
>
> When a guest VM panics, Hyper-V should be notified only once via the
> crash synthetic MSRs. Current Linux code might write these crash MSRs
> twice during a system panic:
> 1) hyperv_panic/die_event() calling hyperv_report_panic()
> 2) hv_kmsg_dump() calling hyperv_report_panic_msg()
>
> Fix this by not calling hyperv_report_panic() if a kmsg dump has been
> successfully registered. The notification will happen later via
> hyperv_report_panic_msg().
>
> Signed-off-by: Tianyu Lan <Tianyu.Lan@xxxxxxxxxxxxx>
> ---
> Change since v1:
> - Update commit log
> ---
> drivers/hv/vmbus_drv.c | 14 ++++++++++++--
> 1 file changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
> index 3a0472c8b7ae..d73fa8aa00a3 100644
> --- a/drivers/hv/vmbus_drv.c
> +++ b/drivers/hv/vmbus_drv.c
> @@ -55,7 +55,12 @@ static int hyperv_panic_event(struct notifier_block *nb, unsigned
> long val,
>
> vmbus_initiate_unload(true);
>
> - if (ms_hyperv.misc_features & HV_FEATURE_GUEST_CRASH_MSR_AVAILABLE) {
> + /*
> + * Crash notify only can be triggered once. If crash notify
> + * message is available, just report kmsg to crash buffer.
> + */
Just to clarify the above comment, let me suggest:
/*
* Hyper-V should be notified only once about a panic. If we will be
* doing hyperv_report_panic_msg() later with kmsg data, don't do
* the notification here.
*/
> + if (ms_hyperv.misc_features & HV_FEATURE_GUEST_CRASH_MSR_AVAILABLE
> + && !hv_panic_page) {
> regs = current_pt_regs();
> hyperv_report_panic(regs, val);
> }
> @@ -68,7 +73,12 @@ static int hyperv_die_event(struct notifier_block *nb, unsigned long
> val,
> struct die_args *die = (struct die_args *)args;
> struct pt_regs *regs = die->regs;
>
> - hyperv_report_panic(regs, val);
> + /*
> + * Crash notify only can be triggered once. If crash notify
> + * message is available, just report kmsg to crash buffer.
> + */
Same suggested clarification to the comment applies here.
> + if (!hv_panic_page)
> + hyperv_report_panic(regs, val);
> return NOTIFY_DONE;
> }
>
> --
> 2.14.5
