Re: [PATCH v14 2/7] ppc: spapr: Introduce FWNMI capability

[Aravinda Prasad]

On Wednesday 25 September 2019 06:42 AM, David Gibson wrote:
> On Wed, Sep 18, 2019 at 01:42:17PM +0530, Aravinda Prasad wrote:
>> Introduce 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 introduces fwnmi-mce capability to
>> deal 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 <address@hidden>
> 
> Mostly ok, but there's one ugly problem.
> 
>> ---
>>  hw/ppc/spapr.c         |    1 +
>>  hw/ppc/spapr_caps.c    |   29 +++++++++++++++++++++++++++++
>>  include/hw/ppc/spapr.h |    4 +++-
>>  target/ppc/kvm.c       |   26 ++++++++++++++++++++++++++
>>  target/ppc/kvm_ppc.h   |   12 ++++++++++++
>>  5 files changed, 71 insertions(+), 1 deletion(-)
>>
>> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
>> index ea56499..8288e8b 100644
>> --- a/hw/ppc/spapr.c
>> +++ b/hw/ppc/spapr.c
>> @@ -4487,6 +4487,7 @@ 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_dual;
>>      smc->dr_phb_enabled = true;
>> diff --git a/hw/ppc/spapr_caps.c b/hw/ppc/spapr_caps.c
>> index 481dfd2..c11ff87 100644
>> --- a/hw/ppc/spapr_caps.c
>> +++ b/hw/ppc/spapr_caps.c
>> @@ -496,6 +496,25 @@ static void cap_ccf_assist_apply(SpaprMachineState 
>> *spapr, uint8_t val,
>>      }
>>  }
>>  
>> +static void cap_fwnmi_mce_apply(SpaprMachineState *spapr, uint8_t val,
>> +                                Error **errp)
>> +{
>> +    if (!val) {
>> +        return; /* Disabled by default */
>> +    }
>> +
>> +    if (tcg_enabled()) {
>> +        /*
>> +         * TCG support may not be correct in some conditions (e.g., in case
>> +         * of software injected faults like duplicate SLBs).
>> +         */
>> +        warn_report("Firmware Assisted Non-Maskable Interrupts not 
>> supported in TCG");
>> +    } else if (kvm_enabled() && !kvmppc_has_cap_ppc_fwnmi()) {
>> +        error_setg(errp,
>> +"Firmware Assisted Non-Maskable Interrupts not supported by KVM, try 
>> cap-fwnmi-mce=off");
>> +    }
>> +}
>> +
>>  SpaprCapabilityInfo capability_table[SPAPR_CAP_NUM] = {
>>      [SPAPR_CAP_HTM] = {
>>          .name = "htm",
>> @@ -595,6 +614,15 @@ 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,
>> @@ -734,6 +762,7 @@ SPAPR_CAP_MIG_STATE(hpt_maxpagesize, 
>> SPAPR_CAP_HPT_MAXPAGESIZE);
>>  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/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
>> index 03111fd..66049ac 100644
>> --- a/include/hw/ppc/spapr.h
>> +++ b/include/hw/ppc/spapr.h
>> @@ -79,8 +79,10 @@ 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 8c5b1f2..8b1ab78 100644
>> --- a/target/ppc/kvm.c
>> +++ b/target/ppc/kvm.c
>> @@ -85,6 +85,7 @@ 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;
>>  
>> @@ -2055,6 +2056,26 @@ void kvmppc_set_mpic_proxy(PowerPCCPU *cpu, int 
>> mpic_proxy)
>>      }
>>  }
>>  
>> +int kvmppc_set_fwnmi(void)
>> +{
>> +    PowerPCCPU *cpu = POWERPC_CPU(first_cpu);
>> +    CPUState *cs = CPU(cpu);
>> +    int ret;
>> +
>> +    ret = kvm_vcpu_enable_cap(cs, KVM_CAP_PPC_FWNMI, 0);
>> +    if (ret) {
>> +        error_report("This KVM version does not support FWNMI");
>> +        return ret;
>> +    }
>> +
>> +    /*
>> +     * cap_ppc_fwnmi is set when FWNMI is available and enabled in KVM
>> +     * and not just when FWNMI is available in KVM
>> +     */
>> +    cap_ppc_fwnmi = 1;
> 
> Using these cap globals is only slighly ugly when they can be
> initialized very early and thereafter remain constant.  However, since
> you're only setting this later (in fact *never* until several patches
> down the series, since kvmppc_set_fwnmi() isn't called), this makes it
> very ugly with this global set at an indeterminite time having effects
> on things the relative order of which is not at all obvious.
> 
> I think it would make much more sense to eliminate the cap_ppc_fwnmi
> global, and instead attempt the enable_cap in cap_fwnmi_mce_apply,
> failing the apply if the enable_cap fails.

ok

> 
>> +    return ret;
>> +}
>> +
>>  int kvmppc_smt_threads(void)
>>  {
>>      return cap_ppc_smt ? cap_ppc_smt : 1;
>> @@ -2355,6 +2376,11 @@ bool kvmppc_has_cap_mmu_hash_v3(void)
>>      return cap_mmu_hash_v3;
>>  }
>>  
>> +bool kvmppc_has_cap_ppc_fwnmi(void)
>> +{
>> +    return cap_ppc_fwnmi;
>> +}
>> +
>>  static bool kvmppc_power8_host(void)
>>  {
>>      bool ret = false;
>> diff --git a/target/ppc/kvm_ppc.h b/target/ppc/kvm_ppc.h
>> index 98bd7d5..ce5c1f9 100644
>> --- a/target/ppc/kvm_ppc.h
>> +++ b/target/ppc/kvm_ppc.h
>> @@ -27,6 +27,8 @@ 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_set_fwnmi(void);
>> +bool kvmppc_has_cap_ppc_fwnmi(void);
>>  int kvmppc_smt_threads(void);
>>  void kvmppc_hint_smt_possible(Error **errp);
>>  int kvmppc_set_smt_threads(int smt);
>> @@ -159,6 +161,16 @@ static inline void kvmppc_set_mpic_proxy(PowerPCCPU 
>> *cpu, int mpic_proxy)
>>  {
>>  }
>>  
>> +static inline int kvmppc_set_fwnmi(void)
>> +{
>> +    return -1;
>> +}
>> +
>> +static inline bool kvmppc_has_cap_ppc_fwnmi(void)
>> +{
>> +    return false;
>> +}
>> +
>>  static inline int kvmppc_smt_threads(void)
>>  {
>>      return 1;
>>
> 

-- 
Regards,
Aravinda