Re: [Qemu-devel] [PATCH v10 6/6] ppc: spapr: Handle "ibm, nmi-register" and "ibm, nmi-interlock" RTAS calls

[Aravinda Prasad <aravinda@linux.vnet.ibm.com>]

On Wednesday 03 July 2019 08:50 AM, David Gibson wrote:
> On Tue, Jul 02, 2019 at 04:10:08PM +0530, Aravinda Prasad wrote:
>>
>>
>> On Tuesday 02 July 2019 09:41 AM, David Gibson wrote:
>>> On Wed, Jun 12, 2019 at 02:51:38PM +0530, Aravinda Prasad wrote:
>>>> This patch adds support in QEMU to handle "ibm,nmi-register"
>>>> and "ibm,nmi-interlock" RTAS calls and sets the default
>>>> value of SPAPR_CAP_FWNMI_MCE to SPAPR_CAP_ON for machine
>>>> type 4.0.
>>>>
>>>> The machine check notification address is saved when the
>>>> OS issues "ibm,nmi-register" RTAS call.
>>>>
>>>> This patch also handles the case when multiple processors
>>>> experience machine check at or about the same time by
>>>> handling "ibm,nmi-interlock" call. In such cases, as per
>>>> PAPR, subsequent processors serialize waiting for the first
>>>> processor to issue the "ibm,nmi-interlock" call. The second
>>>> processor that also received a machine check error waits
>>>> till the first processor is done reading the error log.
>>>> The first processor issues "ibm,nmi-interlock" call
>>>> when the error log is consumed.
>>>>
>>>> Signed-off-by: Aravinda Prasad <aravinda@linux.vnet.ibm.com>
>>>> ---
>>>>  hw/ppc/spapr.c         |    6 ++++-
>>>>  hw/ppc/spapr_rtas.c    |   63 ++++++++++++++++++++++++++++++++++++++++++++++++
>>>>  include/hw/ppc/spapr.h |    5 +++-
>>>>  3 files changed, 72 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
>>>> index 3d6d139..213d493 100644
>>>> --- a/hw/ppc/spapr.c
>>>> +++ b/hw/ppc/spapr.c
>>>> @@ -2946,6 +2946,9 @@ static void spapr_machine_init(MachineState *machine)
>>>>          /* Create the error string for live migration blocker */
>>>>          error_setg(&spapr->fwnmi_migration_blocker,
>>>>                  "Live migration not supported during machine check handling");
>>>> +
>>>> +        /* Register ibm,nmi-register and ibm,nmi-interlock RTAS calls */
>>>> +        spapr_fwnmi_register();
>>>>      }
>>>>  
>>>>      spapr->rtas_blob = g_malloc(spapr->rtas_size);
>>>> @@ -4408,7 +4411,7 @@ static void spapr_machine_class_init(ObjectClass *oc, void *data)
>>>>      smc->default_caps.caps[SPAPR_CAP_NESTED_KVM_HV] = SPAPR_CAP_OFF;
>>>>      smc->default_caps.caps[SPAPR_CAP_LARGE_DECREMENTER] = SPAPR_CAP_ON;
>>>>      smc->default_caps.caps[SPAPR_CAP_CCF_ASSIST] = SPAPR_CAP_OFF;
>>>> -    smc->default_caps.caps[SPAPR_CAP_FWNMI_MCE] = SPAPR_CAP_OFF;
>>>> +    smc->default_caps.caps[SPAPR_CAP_FWNMI_MCE] = SPAPR_CAP_ON;
>>>
>>> Turning this on by default really isn't ok if it stops you running TCG
>>> guests at all.
>>
>> If so this can be "off" by default until TCG is supported.
>>
>>>
>>>>      spapr_caps_add_properties(smc, &error_abort);
>>>>      smc->irq = &spapr_irq_dual;
>>>>      smc->dr_phb_enabled = true;
>>>> @@ -4512,6 +4515,7 @@ static void spapr_machine_3_1_class_options(MachineClass *mc)
>>>>      smc->default_caps.caps[SPAPR_CAP_SBBC] = SPAPR_CAP_BROKEN;
>>>>      smc->default_caps.caps[SPAPR_CAP_IBS] = SPAPR_CAP_BROKEN;
>>>>      smc->default_caps.caps[SPAPR_CAP_LARGE_DECREMENTER] = SPAPR_CAP_OFF;
>>>> +    smc->default_caps.caps[SPAPR_CAP_FWNMI_MCE] = SPAPR_CAP_OFF;
>>>
>>> We're now well past 4.0, and in fact we're about to go into soft
>>> freeze for 4.1, so we're going to miss that too.  So 4.1 and earlier
>>> will need to retain the old default.
>>
>> ok.
>>
>>>
>>>>  }
>>>>  
>>>>  DEFINE_SPAPR_MACHINE(3_1, "3.1", false);
>>>> diff --git a/hw/ppc/spapr_rtas.c b/hw/ppc/spapr_rtas.c
>>>> index a015a80..e010cb2 100644
>>>> --- a/hw/ppc/spapr_rtas.c
>>>> +++ b/hw/ppc/spapr_rtas.c
>>>> @@ -49,6 +49,7 @@
>>>>  #include "hw/ppc/fdt.h"
>>>>  #include "target/ppc/mmu-hash64.h"
>>>>  #include "target/ppc/mmu-book3s-v3.h"
>>>> +#include "migration/blocker.h"
>>>>  
>>>>  static void rtas_display_character(PowerPCCPU *cpu, SpaprMachineState *spapr,
>>>>                                     uint32_t token, uint32_t nargs,
>>>> @@ -352,6 +353,60 @@ static void rtas_get_power_level(PowerPCCPU *cpu, SpaprMachineState *spapr,
>>>>      rtas_st(rets, 1, 100);
>>>>  }
>>>>  
>>>> +static void rtas_ibm_nmi_register(PowerPCCPU *cpu,
>>>> +                                  SpaprMachineState *spapr,
>>>> +                                  uint32_t token, uint32_t nargs,
>>>> +                                  target_ulong args,
>>>> +                                  uint32_t nret, target_ulong rets)
>>>> +{
>>>> +    int ret;
>>>> +    hwaddr rtas_addr = spapr_get_rtas_addr();
>>>> +
>>>> +    if (!rtas_addr) {
>>>> +        rtas_st(rets, 0, RTAS_OUT_NOT_SUPPORTED);
>>>> +        return;
>>>> +    }
>>>> +
>>>> +    if (spapr_get_cap(spapr, SPAPR_CAP_FWNMI_MCE) == SPAPR_CAP_OFF) {
>>>> +        rtas_st(rets, 0, RTAS_OUT_NOT_SUPPORTED);
>>>> +        return;
>>>> +    }
>>>> +
>>>> +    ret = kvmppc_fwnmi_enable(cpu);
>>>> +    if (ret == 1) {
>>>> +        rtas_st(rets, 0, RTAS_OUT_NOT_SUPPORTED);
>>>
>>> I don't understand this case separate from the others.  We've already
>>> set the cap, so fwnmi support should be checked and available.
>>
>> But we have not enabled fwnmi in KVM. kvmppc_fwnmi_enable() returns 1 if
>> cap_ppc_fwnmi is not available in KVM.
> 
> But you've checked for the presence of the extension, yes?  So a
> failure to enable the cap would be unexpected.  In which case how does
> this case differ from.. 

No, this is the function where I check for the presence of the
extension. In kvm_arch_init() we just set cap_ppc_fwnmi to 1 if KVM
support is available, but don't take any action if unavailable.

So this case is when we are running an old version of KVM with no
cap_ppc_fwnmi support.

> 
>>
>>>
>>>> +        return;
>>>> +    } else if (ret < 0) {
>>>> +        error_report("Couldn't enable KVM FWNMI capability");
>>>> +        rtas_st(rets, 0, RTAS_OUT_HW_ERROR);
>>>> +        return;
> 
> ..this case.

And this is when we have the KVM support but due to some problem with
either KVM or QEMU we are unable to enable cap_ppc_fwnmi.

> 
>>>> +    }
>>>> +
>>>> +    spapr->guest_machine_check_addr = rtas_ld(args, 1);
>>>> +    rtas_st(rets, 0, RTAS_OUT_SUCCESS);
>>>> +}
>>>> +
>>>> +static void rtas_ibm_nmi_interlock(PowerPCCPU *cpu,
>>>> +                                   SpaprMachineState *spapr,
>>>> +                                   uint32_t token, uint32_t nargs,
>>>> +                                   target_ulong args,
>>>> +                                   uint32_t nret, target_ulong rets)
>>>> +{
>>>> +    if (spapr->guest_machine_check_addr == -1) {
>>>> +        /* NMI register not called */
>>>> +        rtas_st(rets, 0, RTAS_OUT_PARAM_ERROR);
>>>> +    } else {
>>>> +        /*
>>>> +         * vCPU issuing "ibm,nmi-interlock" is done with NMI handling,
>>>> +         * hence unset mc_status.
>>>> +         */
>>>> +        spapr->mc_status = -1;
>>>> +        qemu_cond_signal(&spapr->mc_delivery_cond);
>>>> +        migrate_del_blocker(spapr->fwnmi_migration_blocker);
>>>
>>> Hrm.  We add the blocker at the mce request point.  First, that's in
>>> another patch, which isn't great.  Second, does that mean we could add
>>> multiple times if we get an MCE on multiple CPUs?  Will that work and
>>> correctly match adds and removes properly?
>>
>> If it is fine to move the migration patch as the last patch in the
>> sequence, then we will have add and del blocker in the same patch.
>>
>> And yes we could add multiple times if we get MCE on multiple CPUs and
>> as all those cpus call interlock there should be matching number of
>> delete blockers.
> 
> Ok, and I think adding the same pointer to the list multiple times
> will work ok.

I think so

> 
> Btw, add_blocker() can fail - have you handled failure conditions?

yes, I am handling it.

> 

-- 
Regards,
Aravinda