Re: [PATCH v7 2/3] powerpc/powernv: Introduce a machine check hook for Guest MCEs.

From: Michael Ellerman <mpe@ellerman.id.au>
To: Mahesh J Salgaonkar <mahesh@linux.vnet.ibm.com>,
	gleb@kernel.org, agraf@suse.de, KVM-PPC <kvm-ppc@vger.kernel.org>,
	linuxppc-dev <linuxppc-dev@ozlabs.org>,
	Paul Mackerras <paulus@samba.org>,
	pbonzini@redhat.com
Cc: KVM <kvm@vger.kernel.org>, david@gibson.dropbear.id.au
Subject: Re: [PATCH v7 2/3] powerpc/powernv: Introduce a machine check hook for Guest MCEs.
Date: Thu, 06 Apr 2017 15:53:53 +1000	[thread overview]
Message-ID: <878tneuln2.fsf@concordia.ellerman.id.au> (raw)
In-Reply-To: <149142524189.28284.14876788789820474952.stgit@jupiter.in.ibm.com>

Mahesh J Salgaonkar <mahesh@linux.vnet.ibm.com> writes:

> From: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
>
> This patch introduces a mce hook which is invoked at the time of guest
> exit to facilitate the host-side handling of machine check exception
> before the exception is passed on to the guest. This hook will be invoked
> from host virtual mode from KVM (before exiting the guest with
> KVM_EXIT_NMI reason) for machine check exception that occurs in the guest.

Hi Mahesh,

This patch doesn't meaningfully abstract anything.

opal_machine_check_guest() doesn't call opal, or do anything opal
specific. It just passes the evt struct back to code in mce.c, which is
where the struct came from in the first place.

> --- a/arch/powerpc/platforms/powernv/opal.c
> +++ b/arch/powerpc/platforms/powernv/opal.c
> @@ -479,6 +479,32 @@ int opal_machine_check(struct pt_regs *regs)
>  	return 0;
>  }
>  
> +#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
> +/*
> + * opal_machine_check_guest() is a hook which is invoked at the time
> + * of guest exit to facilitate the host-side handling of machine check
> + * exception before the exception is passed on to the guest. This hook
> + * is invoked from host virtual mode from KVM (before exiting the guest
> + * with KVM_EXIT_NMI reason) for machine check exception that occurs in
> + * the guest.
> + *
> + * Currently no action is performed in the host other than printing the
> + * event information. The machine check exception is passed on to the
> + * guest kernel and the guest kernel will attempt for recovery.
> + */
> +int opal_machine_check_guest(struct machine_check_event *evt)
> +{
> +	/* Print things out */
> +	if (evt->version != MCE_V1) {
> +		pr_err("Machine Check Exception, Unknown event version %d !\n",
> +		       evt->version);
> +		return 0;
> +	}
> +	machine_check_print_event_info(evt);
> +	return 0;
> +}
> +#endif

Called from kvmppc_handle_exit_hv():

+		if (ppc_md.machine_check_exception_guest)
+			ppc_md.machine_check_exception_guest(
+							&vcpu->arch.mce_evt);
 		break;

Just call machine_check_print_event_info() directly from
kvmppc_handle_exit_hv().

You'll need to export symbol it, but that's all AFAICS, I don't think it
even needs any #ifdefs.

If we ever want to do anything different we can change the code then.

cheers