Re: [Qemu-devel] [Qemu-ppc] [PATCH v8 5/6] ppc: spapr: Enable FWNMI capability

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

On Friday 10 May 2019 03:23 PM, David Gibson wrote:
> On Fri, May 10, 2019 at 12:45:29PM +0530, Aravinda Prasad wrote:
>>
>>
>> On Friday 10 May 2019 12:16 PM, David Gibson wrote:
>>> On Mon, Apr 22, 2019 at 12:33:35PM +0530, Aravinda Prasad wrote:
>>>> Enable the KVM capability KVM_CAP_PPC_FWNMI so that
>>>> the KVM causes guest exit with NMI as exit reason
>>>> when it encounters a machine check exception on the
>>>> address belonging to a guest. Without this capability
>>>> enabled, KVM redirects machine check exceptions to
>>>> guest's 0x200 vector.
>>>>
>>>> This patch also deals with the case when a guest with
>>>> the KVM_CAP_PPC_FWNMI capability enabled is attempted
>>>> to migrate to a host that does not support this
>>>> capability.
>>>>
>>>> Signed-off-by: Aravinda Prasad <aravinda@linux.vnet.ibm.com>
>>>> ---
>>>>  hw/ppc/spapr.c         |    1 +
>>>>  hw/ppc/spapr_caps.c    |   26 ++++++++++++++++++++++++++
>>>>  hw/ppc/spapr_rtas.c    |   14 ++++++++++++++
>>>>  include/hw/ppc/spapr.h |    4 +++-
>>>>  target/ppc/kvm.c       |   14 ++++++++++++++
>>>>  target/ppc/kvm_ppc.h   |    6 ++++++
>>>>  6 files changed, 64 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
>>>> index ffd1715..44e09bb 100644
>>>> --- a/hw/ppc/spapr.c
>>>> +++ b/hw/ppc/spapr.c
>>>> @@ -4372,6 +4372,7 @@ 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;
>>>>      spapr_caps_add_properties(smc, &error_abort);
>>>>      smc->irq = &spapr_irq_xics;
>>>>      smc->dr_phb_enabled = true;
>>>> diff --git a/hw/ppc/spapr_caps.c b/hw/ppc/spapr_caps.c
>>>> index edc5ed0..5b3af04 100644
>>>> --- a/hw/ppc/spapr_caps.c
>>>> +++ b/hw/ppc/spapr_caps.c
>>>> @@ -473,6 +473,22 @@ static void cap_ccf_assist_apply(SpaprMachineState *spapr, uint8_t val,
>>>>      }
>>>>  }
>>>>  
>>>> +static void cap_fwnmi_mce_apply(SpaprMachineState *spapr, uint8_t val,
>>>> +                                Error **errp)
>>>> +{
>>>> +    PowerPCCPU *cpu = POWERPC_CPU(first_cpu);
>>>> +
>>>> +    if (!val) {
>>>> +        return; /* Disabled by default */
>>>> +    }
>>>> +
>>>> +    if (kvm_enabled()) {
>>>> +        if (kvmppc_fwnmi_enable(cpu)) {
>>>> +            error_setg(errp, "Requested fwnmi capability not support by KVM");
>>>> +        }
>>>> +    }
>>>> +}
>>>> +
>>>>  SpaprCapabilityInfo capability_table[SPAPR_CAP_NUM] = {
>>>>      [SPAPR_CAP_HTM] = {
>>>>          .name = "htm",
>>>> @@ -571,6 +587,15 @@ SpaprCapabilityInfo capability_table[SPAPR_CAP_NUM] = {
>>>>          .type = "bool",
>>>>          .apply = cap_ccf_assist_apply,
>>>>      },
>>>> +    [SPAPR_CAP_FWNMI_MCE] = {
>>>> +        .name = "fwnmi-mce",
>>>> +        .description = "Handle fwnmi machine check exceptions",
>>>> +        .index = SPAPR_CAP_FWNMI_MCE,
>>>> +        .get = spapr_cap_get_bool,
>>>> +        .set = spapr_cap_set_bool,
>>>> +        .type = "bool",
>>>> +        .apply = cap_fwnmi_mce_apply,
>>>> +    },
>>>>  };
>>>>  
>>>>  static SpaprCapabilities default_caps_with_cpu(SpaprMachineState *spapr,
>>>> @@ -706,6 +731,7 @@ SPAPR_CAP_MIG_STATE(ibs, SPAPR_CAP_IBS);
>>>>  SPAPR_CAP_MIG_STATE(nested_kvm_hv, SPAPR_CAP_NESTED_KVM_HV);
>>>>  SPAPR_CAP_MIG_STATE(large_decr, SPAPR_CAP_LARGE_DECREMENTER);
>>>>  SPAPR_CAP_MIG_STATE(ccf_assist, SPAPR_CAP_CCF_ASSIST);
>>>> +SPAPR_CAP_MIG_STATE(fwnmi, SPAPR_CAP_FWNMI_MCE);
>>>>  
>>>>  void spapr_caps_init(SpaprMachineState *spapr)
>>>>  {
>>>> diff --git a/hw/ppc/spapr_rtas.c b/hw/ppc/spapr_rtas.c
>>>> index d3499f9..997cf19 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 "kvm_ppc.h"
>>>>  
>>>>  static void rtas_display_character(PowerPCCPU *cpu, SpaprMachineState *spapr,
>>>>                                     uint32_t token, uint32_t nargs,
>>>> @@ -354,6 +355,7 @@ static void rtas_ibm_nmi_register(PowerPCCPU *cpu,
>>>>                                    target_ulong args,
>>>>                                    uint32_t nret, target_ulong rets)
>>>>  {
>>>> +    int ret;
>>>>      uint64_t rtas_addr = spapr_get_rtas_addr();
>>>>  
>>>>      if (!rtas_addr) {
>>>> @@ -361,6 +363,18 @@ static void rtas_ibm_nmi_register(PowerPCCPU *cpu,
>>>>          return;
>>>>      }
>>>>  
>>>> +    ret = kvmppc_fwnmi_enable(cpu);
>>>
>>> You shouldn't need this here as well as in cap_fwnmi_mce_apply().
>>>
>>> Instead, you should unconditionally fail the nmi-register if the
>>> capability is not enabled.
>>
>> cap_fwnmi is not enabled by default, because if it is enabled by default
>> them KVM will start routing machine check exceptions via guest exit
>> instead of routing it to guest's 0x200.
>>
>> During early boot since guest has not yet issued nmi-register, KVM is
>> expected to route exceptions to 0x200. Therefore we enable cap_fwnmi
>> only when a guest issues nmi-register.
> 
> Except that's not true - you enable it in cap_fwnmi_mce_apply() which
> will be executed whenever the machine capability is enabled.

I enable cap_fwnmi in cap_fwnmi_mce_apply() only when the "val" argument
(which is the effective cap value) is set. In early boot "val" is not
set as cap_fwnmi by default is not set, hence cap_fwnmi is not enabled.

My understanding is that, cap_fwnmi_mce_apply() is also called during
migration on the target machine. If effective cap for cap_fwnmi is
enabled on source machine than I think "val" will be set when
cap_fwnmi_mce_apply() is called on target machine. I then call
kvmppc_fwnmi_enable() to enable cap_fwnmi on target.

Regards,
Aravinda

> 
>> Or we should take the approach of enabling this capability by default
>> and then from QEMU route the error to 0x200 if guest has not issued
>> nmi-register.
>>
>>>
>>>> +    if (ret == 1) {
>>>> +        rtas_st(rets, 0, RTAS_OUT_NOT_SUPPORTED);
>>>> +        return;
>>>> +    }
>>>> +
>>>> +    if (ret < 0) {
>>>> +        rtas_st(rets, 0, RTAS_OUT_HW_ERROR);
>>>> +        return;
>>>> +    }
>>>> +
>>>>      spapr->guest_machine_check_addr = rtas_ld(args, 1);
>>>>      rtas_st(rets, 0, RTAS_OUT_SUCCESS);
>>>>  }
>>>> diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
>>>> index 03f34bf..9d16ad1 100644
>>>> --- a/include/hw/ppc/spapr.h
>>>> +++ b/include/hw/ppc/spapr.h
>>>> @@ -78,8 +78,10 @@ typedef enum {
>>>>  #define SPAPR_CAP_LARGE_DECREMENTER     0x08
>>>>  /* Count Cache Flush Assist HW Instruction */
>>>>  #define SPAPR_CAP_CCF_ASSIST            0x09
>>>> +/* FWNMI machine check handling */
>>>> +#define SPAPR_CAP_FWNMI_MCE             0x0A
>>>>  /* Num Caps */
>>>> -#define SPAPR_CAP_NUM                   (SPAPR_CAP_CCF_ASSIST + 1)
>>>> +#define SPAPR_CAP_NUM                   (SPAPR_CAP_FWNMI_MCE + 1)
>>>>  
>>>>  /*
>>>>   * Capability Values
>>>> diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
>>>> index 5eedce8..9c7b71d 100644
>>>> --- a/target/ppc/kvm.c
>>>> +++ b/target/ppc/kvm.c
>>>> @@ -83,6 +83,7 @@ static int cap_ppc_safe_indirect_branch;
>>>>  static int cap_ppc_count_cache_flush_assist;
>>>>  static int cap_ppc_nested_kvm_hv;
>>>>  static int cap_large_decr;
>>>> +static int cap_ppc_fwnmi;
>>>>  
>>>>  static uint32_t debug_inst_opcode;
>>>>  
>>>> @@ -150,6 +151,7 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
>>>>      kvmppc_get_cpu_characteristics(s);
>>>>      cap_ppc_nested_kvm_hv = kvm_vm_check_extension(s, KVM_CAP_PPC_NESTED_HV);
>>>>      cap_large_decr = kvmppc_get_dec_bits();
>>>> +    cap_ppc_fwnmi = kvm_check_extension(s, KVM_CAP_PPC_FWNMI);
>>>>      /*
>>>>       * Note: setting it to false because there is not such capability
>>>>       * in KVM at this moment.
>>>> @@ -2117,6 +2119,18 @@ void kvmppc_set_mpic_proxy(PowerPCCPU *cpu, int mpic_proxy)
>>>>      }
>>>>  }
>>>>  
>>>> +int kvmppc_fwnmi_enable(PowerPCCPU *cpu)
>>>> +{
>>>> +    CPUState *cs = CPU(cpu);
>>>> +
>>>> +    if (!cap_ppc_fwnmi) {
>>>> +        return 1;
>>>> +    }
>>>> +
>>>> +    return kvm_vcpu_enable_cap(cs, KVM_CAP_PPC_FWNMI, 0);
>>>> +}
>>>> +
>>>> +
>>>>  int kvmppc_smt_threads(void)
>>>>  {
>>>>      return cap_ppc_smt ? cap_ppc_smt : 1;
>>>> diff --git a/target/ppc/kvm_ppc.h b/target/ppc/kvm_ppc.h
>>>> index 6edc42f..28919d3 100644
>>>> --- a/target/ppc/kvm_ppc.h
>>>> +++ b/target/ppc/kvm_ppc.h
>>>> @@ -27,6 +27,7 @@ void kvmppc_enable_h_page_init(void);
>>>>  void kvmppc_set_papr(PowerPCCPU *cpu);
>>>>  int kvmppc_set_compat(PowerPCCPU *cpu, uint32_t compat_pvr);
>>>>  void kvmppc_set_mpic_proxy(PowerPCCPU *cpu, int mpic_proxy);
>>>> +int kvmppc_fwnmi_enable(PowerPCCPU *cpu);
>>>>  int kvmppc_smt_threads(void);
>>>>  void kvmppc_hint_smt_possible(Error **errp);
>>>>  int kvmppc_set_smt_threads(int smt);
>>>> @@ -159,6 +160,11 @@ static inline void kvmppc_set_mpic_proxy(PowerPCCPU *cpu, int mpic_proxy)
>>>>  {
>>>>  }
>>>>  
>>>> +static inline int kvmppc_fwnmi_enable(PowerPCCPU *cpu)
>>>> +{
>>>> +    return 1;
>>>> +}
>>>> +
>>>>  static inline int kvmppc_smt_threads(void)
>>>>  {
>>>>      return 1;
>>>>
>>>
>>
> 

-- 
Regards,
Aravinda