Re: [PATCH 2/2] target/ppc/kvm: Use KVM_CAP_PPC_AIL_MODE_3 to determine cap-ail-mode-3 support

[Fabiano Rosas <farosas@linux.ibm.com>]

Nicholas Piggin <npiggin@gmail.com> writes:

> Use KVM_CAP_PPC_AIL_MODE_3 to determine cap-ail-mode-3 support for KVM
> guests. Keep the fallback heuristic for KVM hosts that pre-date this
> CAP.
>
> This is only proposed the KVM CAP has not yet been allocated. I will
> ask to merge the new KVM cap when there are no objections on the QEMU
> side.
>
> not-yet-Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> ---
>  hw/ppc/spapr_caps.c       |  2 +-
>  linux-headers/linux/kvm.h |  1 +
>  target/ppc/kvm.c          | 18 +++++++++++++++++-
>  target/ppc/kvm_ppc.h      |  4 ++--
>  4 files changed, 21 insertions(+), 4 deletions(-)
>
> diff --git a/hw/ppc/spapr_caps.c b/hw/ppc/spapr_caps.c
> index 5fd4a53c33..5cc80776d0 100644
> --- a/hw/ppc/spapr_caps.c
> +++ b/hw/ppc/spapr_caps.c
> @@ -619,7 +619,7 @@ static void cap_ail_mode_3_apply(SpaprMachineState *spapr,
>      ERRP_GUARD();
>  
>      if (kvm_enabled()) {
> -        if (!kvmppc_supports_ail_3()) {
> +        if (!kvmppc_has_cap_ail_3()) {
>              error_setg(errp, "KVM implementation does not support cap-ail-mode-3");
>              error_append_hint(errp, "Try appending -machine cap-ail-mode-3=off\n");
>              return;
> diff --git a/linux-headers/linux/kvm.h b/linux-headers/linux/kvm.h
> index 02c5e7b7bb..d91f578200 100644
> --- a/linux-headers/linux/kvm.h
> +++ b/linux-headers/linux/kvm.h
> @@ -1130,6 +1130,7 @@ struct kvm_ppc_resize_hpt {
>  #define KVM_CAP_BINARY_STATS_FD 203
>  #define KVM_CAP_EXIT_ON_EMULATION_FAILURE 204
>  #define KVM_CAP_ARM_MTE 205
> +#define KVM_CAP_PPC_AIL_MODE_3 210
>  
>  #ifdef KVM_CAP_IRQ_ROUTING
>  
> diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
> index 128bc530d4..d0d0bdaac4 100644
> --- a/target/ppc/kvm.c
> +++ b/target/ppc/kvm.c
> @@ -90,6 +90,7 @@ static int cap_ppc_nested_kvm_hv;
>  static int cap_large_decr;
>  static int cap_fwnmi;
>  static int cap_rpt_invalidate;
> +static int cap_ail_mode_3;
>  
>  static uint32_t debug_inst_opcode;
>  
> @@ -154,6 +155,7 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
>      }
>  
>      cap_rpt_invalidate = kvm_vm_check_extension(s, KVM_CAP_PPC_RPT_INVALIDATE);
> +    cap_ail_mode_3 = kvm_vm_check_extension(s, KVM_CAP_PPC_AIL_MODE_3);
>      kvm_ppc_register_host_cpu_type();
>  
>      return 0;
> @@ -2563,10 +2565,24 @@ int kvmppc_has_cap_rpt_invalidate(void)
>      return cap_rpt_invalidate;
>  }
>  
> -int kvmppc_supports_ail_3(void)
> +int kvmppc_has_cap_ail_3(void)
>  {
>      PowerPCCPUClass *pcc = kvm_ppc_get_host_cpu_class();
>  
> +    if (cap_ail_mode_3) {
> +        return 1;
> +    }
> +
> +    if (kvm_ioctl(kvm_state, KVM_CHECK_EXTENSION, KVM_CAP_PPC_AIL_MODE_3) == 0) {
> +        return 0;
> +    }

This is not needed here it seems.

> +
> +    /*
> +     * For KVM hosts that pre-date this cap, special-case the test because
> +     * the performance cost for disabling the feature unconditionally is
> +     * prohibitive.
> +     */
> +
>      /*
>       * KVM PR only supports AIL-0
>       */
> diff --git a/target/ppc/kvm_ppc.h b/target/ppc/kvm_ppc.h
> index d9d1c54955..efafa67b83 100644
> --- a/target/ppc/kvm_ppc.h
> +++ b/target/ppc/kvm_ppc.h
> @@ -73,7 +73,7 @@ int kvmppc_set_cap_nested_kvm_hv(int enable);
>  int kvmppc_get_cap_large_decr(void);
>  int kvmppc_enable_cap_large_decr(PowerPCCPU *cpu, int enable);
>  int kvmppc_has_cap_rpt_invalidate(void);
> -int kvmppc_supports_ail_3(void);
> +int kvmppc_has_cap_ail_3(void);
>  int kvmppc_enable_hwrng(void);
>  int kvmppc_put_books_sregs(PowerPCCPU *cpu);
>  PowerPCCPUClass *kvm_ppc_get_host_cpu_class(void);
> @@ -394,7 +394,7 @@ static inline int kvmppc_has_cap_rpt_invalidate(void)
>      return false;
>  }
>  
> -static inline int kvmppc_supports_ail_3(void)
> +static inline int kvmppc_has_cap_ail_3(void)
>  {
>      return false;
>  }