Re: [Qemu-devel] [PATCH v7 5/6] ppc: spapr: Enable FWNMI capability

[David Gibson]

On Fri, Mar 22, 2019 at 12:04:16PM +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.
> 
> Signed-off-by: Aravinda Prasad <address@hidden>
> ---
>  hw/ppc/spapr_rtas.c  |   15 +++++++++++++++
>  target/ppc/kvm.c     |   14 ++++++++++++++
>  target/ppc/kvm_ppc.h |    6 ++++++
>  3 files changed, 35 insertions(+)
> 
> diff --git a/hw/ppc/spapr_rtas.c b/hw/ppc/spapr_rtas.c
> index fb594a4..939f428 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 +355,20 @@ static void rtas_ibm_nmi_register(PowerPCCPU *cpu,
>                                    target_ulong args,
>                                    uint32_t nret, target_ulong rets)
>  {
> +    int ret;
> +
> +    ret = kvmppc_fwnmi_enable(cpu);
> +
> +    if (ret == 1) {
> +        rtas_st(rets, 0, RTAS_OUT_NOT_SUPPORTED);

Urgh, we're here making a guest visible different to the environment
depending on a host (KVM) capability.  What happens if you start a
guest and it registers fwnmi support, then migrate it to a host that
lacks the necessary KVM support?

> +        return;
> +    }
> +
> +    if (ret < 0) {
> +        rtas_st(rets, 0, RTAS_OUT_HW_ERROR);
> +        return;
> +    }
> +
>      spapr->mc_reset = 0;
>      spapr->guest_machine_check_addr = rtas_ld(args, 1);
>      rtas_st(rets, 0, RTAS_OUT_SUCCESS);
> diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
> index a593448..161b45e 100644
> --- a/target/ppc/kvm.c
> +++ b/target/ppc/kvm.c
> @@ -93,6 +93,7 @@ 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;
>  
> @@ -155,6 +156,7 @@ 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.
> @@ -2091,6 +2093,18 @@ 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 df5e85f..cf7b24f 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);
> @@ -158,6 +159,11 @@ static inline void kvmppc_set_mpic_proxy(PowerPCCPU 
> *cpu, int mpic_proxy)
>  {
>  }
>  
> +int kvmppc_fwnmi_enable(PowerPCCPU *cpu)
> +{
> +    return 1;
> +}
> +
>  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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