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

[Mahesh Jagannath Salgaonkar <mahesh@linux.vnet.ibm.com>]

On 04/06/2017 10:52 AM, David Gibson wrote:
> On Thu, Apr 06, 2017 at 02:17:22AM +0530, Mahesh J Salgaonkar wrote:
>> 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.
>>
>> Signed-off-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
> 
> Um.. this introduces the hook, and puts in an implementation of it,
> but AFAICT, nothing calls it, either here or in the next patch.  That
> seems a bit pointless.

It gets called in the next patch [3/3] through
ppc_md.machine_check_exception_guest(). See the hunk for file
arch/powerpc/kvm/book3s_hv.c in next patch.

> 
>> ---
>>  arch/powerpc/include/asm/machdep.h     |    7 +++++++
>>  arch/powerpc/include/asm/opal.h        |    4 ++++
>>  arch/powerpc/platforms/powernv/opal.c  |   26 ++++++++++++++++++++++++++
>>  arch/powerpc/platforms/powernv/setup.c |    3 +++
>>  4 files changed, 40 insertions(+)
>>
>> diff --git a/arch/powerpc/include/asm/machdep.h b/arch/powerpc/include/asm/machdep.h
>> index 5011b69..9d74e7a 100644
>> --- a/arch/powerpc/include/asm/machdep.h
>> +++ b/arch/powerpc/include/asm/machdep.h
>> @@ -15,6 +15,7 @@
>>  #include <linux/export.h>
>>  
>>  #include <asm/setup.h>
>> +#include <asm/mce.h>
>>  
>>  /* We export this macro for external modules like Alsa to know if
>>   * ppc_md.feature_call is implemented or not
>> @@ -112,6 +113,12 @@ struct machdep_calls {
>>  	/* Called during machine check exception to retrive fixup address. */
>>  	bool		(*mce_check_early_recovery)(struct pt_regs *regs);
>>  
>> +#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
>> +	/* Called after KVM interrupt handler finishes handling MCE for guest */
>> +	int		(*machine_check_exception_guest)
>> +					(struct machine_check_event *evt);
>> +#endif
>> +
>>  	/* Motherboard/chipset features. This is a kind of general purpose
>>  	 * hook used to control some machine specific features (like reset
>>  	 * lines, chip power control, etc...).
>> diff --git a/arch/powerpc/include/asm/opal.h b/arch/powerpc/include/asm/opal.h
>> index 1ff03a6..9b1fcbf 100644
>> --- a/arch/powerpc/include/asm/opal.h
>> +++ b/arch/powerpc/include/asm/opal.h
>> @@ -17,6 +17,7 @@
>>  #ifndef __ASSEMBLY__
>>  
>>  #include <linux/notifier.h>
>> +#include <asm/mce.h>
>>  
>>  /* We calculate number of sg entries based on PAGE_SIZE */
>>  #define SG_ENTRIES_PER_NODE ((PAGE_SIZE - 16) / sizeof(struct opal_sg_entry))
>> @@ -273,6 +274,9 @@ extern int opal_hmi_handler_init(void);
>>  extern int opal_event_init(void);
>>  
>>  extern int opal_machine_check(struct pt_regs *regs);
>> +#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
>> +extern int opal_machine_check_guest(struct machine_check_event *evt);
>> +#endif
>>  extern bool opal_mce_check_early_recovery(struct pt_regs *regs);
>>  extern int opal_hmi_exception_early(struct pt_regs *regs);
>>  extern int opal_handle_hmi_exception(struct pt_regs *regs);
>> diff --git a/arch/powerpc/platforms/powernv/opal.c b/arch/powerpc/platforms/powernv/opal.c
>> index e0f856b..5e633a4 100644
>> --- 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
>> +
>>  /* Early hmi handler called in real mode. */
>>  int opal_hmi_exception_early(struct pt_regs *regs)
>>  {
>> diff --git a/arch/powerpc/platforms/powernv/setup.c b/arch/powerpc/platforms/powernv/setup.c
>> index d50c7d9..333ee09 100644
>> --- a/arch/powerpc/platforms/powernv/setup.c
>> +++ b/arch/powerpc/platforms/powernv/setup.c
>> @@ -264,6 +264,9 @@ static void __init pnv_setup_machdep_opal(void)
>>  	ppc_md.mce_check_early_recovery = opal_mce_check_early_recovery;
>>  	ppc_md.hmi_exception_early = opal_hmi_exception_early;
>>  	ppc_md.handle_hmi_exception = opal_handle_hmi_exception;
>> +#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
>> +	ppc_md.machine_check_exception_guest = opal_machine_check_guest;
>> +#endif
>>  }
>>  
>>  static int __init pnv_probe(void)
>>
>