RE: [PATCH v11 2/5] arm64: hyperv: Add panic handler

[Sunil Muthuswamy <sunilmut@microsoft.com>]

> Add a function to inform Hyper-V about a guest panic.
> 
> This code is built only when CONFIG_HYPERV is enabled.
> 
> Signed-off-by: Michael Kelley <mikelley@microsoft.com>
> ---
>  arch/arm64/hyperv/hv_core.c | 52 +++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 52 insertions(+)
> 
> diff --git a/arch/arm64/hyperv/hv_core.c b/arch/arm64/hyperv/hv_core.c
> index 4c5dc0f..b54c347 100644
> --- a/arch/arm64/hyperv/hv_core.c
> +++ b/arch/arm64/hyperv/hv_core.c
> @@ -127,3 +127,55 @@ u64 hv_get_vpreg(u32 msr)
>  	return output.as64.low;
>  }
>  EXPORT_SYMBOL_GPL(hv_get_vpreg);
> +
> +/*
> + * hyperv_report_panic - report a panic to Hyper-V.  This function uses
> + * the older version of the Hyper-V interface that admittedly doesn't
> + * pass enough information to be useful beyond just recording the
> + * occurrence of a panic. The parallel hv_kmsg_dump() uses the
> + * new interface that allows reporting 4 Kbytes of data, which is much
> + * more useful. Hyper-V on ARM64 always supports the newer interface, but
> + * we retain support for the older version because the sysadmin is allowed
> + * to disable the newer version via sysctl in case of information security
> + * concerns about the more verbose version.
> + */
> +void hyperv_report_panic(struct pt_regs *regs, long err, bool in_die)
> +{
> +	static bool	panic_reported;
> +	u64		guest_id;
> +
> +	/* Don't report a panic to Hyper-V if we're not going to panic */
> +	if (in_die && !panic_on_oops)
> +		return;
> +
> +	/*
> +	 * We prefer to report panic on 'die' chain as we have proper
> +	 * registers to report, but if we miss it (e.g. on BUG()) we need
> +	 * to report it on 'panic'.
> +	 *
> +	 * Calling code in the 'die' and 'panic' paths ensures that only
> +	 * one CPU is running this code, so no atomicity is needed.
> +	 */
> +	if (panic_reported)
> +		return;
> +	panic_reported = true;
> +
> +	guest_id = hv_get_vpreg(HV_REGISTER_GUEST_OSID);
> +
> +	/*
> +	 * Hyper-V provides the ability to store only 5 values.
> +	 * Pick the passed in error value, the guest_id, the PC,
> +	 * and the SP.
> +	 */
> +	hv_set_vpreg(HV_REGISTER_CRASH_P0, err);
> +	hv_set_vpreg(HV_REGISTER_CRASH_P1, guest_id);
> +	hv_set_vpreg(HV_REGISTER_CRASH_P2, regs->pc);
> +	hv_set_vpreg(HV_REGISTER_CRASH_P3, regs->sp);
> +	hv_set_vpreg(HV_REGISTER_CRASH_P4, 0);
> +
> +	/*
> +	 * Let Hyper-V know there is crash data available
> +	 */
> +	hv_set_vpreg(HV_REGISTER_CRASH_CTL, HV_CRASH_CTL_CRASH_NOTIFY);
> +}
> +EXPORT_SYMBOL_GPL(hyperv_report_panic);
> --
> 1.8.3.1

Reviewed-by: Sunil Muthuswamy <sunilmut@microsoft.com>