RE: [PATCH 4/4] x86/Hyper-V: Report crash register data or ksmg before running crash kernel

[Michael Kelley]

From: ltykernel@xxxxxxxxx <ltykernel@xxxxxxxxx>  Sent: Tuesday, March 17, 2020 6:25 AM
> 
> Hyper-V expects to get crash register data or kmsg via crash
> enlightenment when guest crash happens. crash_kexec_post_notifiers
> is default to be false and crash kernel runs before calling hv
> panic callback and dumping kmsg. In this case, Hyper-V doesn't
> get crash register data or kmsg from guest. Set crash_kexec_post
> _notifiers to be true for Hyper-V VM and fix it.

Suggested wording tweaks:

We want to notify Hyper-V when a Linux guest VM crash occurs, so
there is a record of the crash even when kdump is enabled.   But
crash_kexec_post_notifiers defaults to "false", so the kdump kernel
runs before the notifiers and Hyper-V never gets notified.  Fix this by
always setting crash_kexec_post_notifiers to be true for Hyper-V VMs.

> 
> Signed-off-by: Tianyu Lan <Tianyu.Lan@xxxxxxxxxxxxx>
> ---
>  arch/x86/kernel/cpu/mshyperv.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
> index caa032ce3fe3..5e296a7e6036 100644
> --- a/arch/x86/kernel/cpu/mshyperv.c
> +++ b/arch/x86/kernel/cpu/mshyperv.c
> @@ -263,6 +263,16 @@ static void __init ms_hyperv_init_platform(void)
>  			cpuid_eax(HYPERV_CPUID_NESTED_FEATURES);
>  	}
> 
> +	/*
> +	 * Hyper-V expects to get crash register data or kmsg when
> +	 * crash enlightment is available and system crashes. Set
> +	 * crash_kexec_post_notifiers to be true to make sure that
> +	 * calling crash enlightment interface before running kdump
> +	 * kernel.
> +	 */
> +	if (ms_hyperv.misc_features & HV_FEATURE_GUEST_CRASH_MSR_AVAILABLE)
> +		crash_kexec_post_notifiers = true;
> +
>  #ifdef CONFIG_X86_LOCAL_APIC
>  	if (ms_hyperv.features & HV_X64_ACCESS_FREQUENCY_MSRS &&
>  	    ms_hyperv.misc_features & HV_FEATURE_FREQUENCY_MSRS_AVAILABLE) {
> --
> 2.14.5