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

[David Gibson <david@gibson.dropbear.id.au>]

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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 <aravinda@linux.vnet.ibm.com>

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.

> +    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;
> 

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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