Re: [Qemu-devel] [QEMU-PPC] [PATCH 2/2] target/ppc/spapr: Add SPAPR_CAP_CCF_ASSIST

[Suraj Jitindar Singh <sjitindarsingh@gmail.com>]

On Fri, 2019-03-01 at 14:19 +1100, Suraj Jitindar Singh wrote:
> Introduce a new spapr_cap SPAPR_CAP_CCF_ASSIST to be used to indicate
> the requirement for a hw-assisted version of the count cache flush
> workaround.
> 
> The count cache flush workaround is a software workaround which can
> be
> used to flush the count cache on context switch. Some revisions of
> hardware may have a hardware accelerated flush, in which case the
> software flush can be shortened. This cap is used to set the
> availability of such hardware acceleration for the count cache flush
> routine.
> 
> The availability of such hardware acceleration is indicated by the
> H_CPU_CHAR_BCCTR_FLUSH_ASSIST flag being set in the characteristics
> returned from the KVM_PPC_GET_CPU_CHAR ioctl.
> 
> Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
> ---
>  hw/ppc/spapr.c         |  2 ++
>  hw/ppc/spapr_caps.c    | 25 +++++++++++++++++++++++++
>  hw/ppc/spapr_hcall.c   |  3 +++
>  include/hw/ppc/spapr.h |  5 ++++-
>  target/ppc/kvm.c       | 14 ++++++++++++++
>  target/ppc/kvm_ppc.h   |  6 ++++++
>  6 files changed, 54 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 1df324379f..708e18dcdf 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -2086,6 +2086,7 @@ static const VMStateDescription vmstate_spapr =
> {
>          &vmstate_spapr_cap_nested_kvm_hv,
>          &vmstate_spapr_dtb,
>          &vmstate_spapr_cap_large_decr,
> +        &vmstate_spapr_cap_ccf_assist,
>          NULL
>      }
>  };
> @@ -4319,6 +4320,7 @@ static void
> spapr_machine_class_init(ObjectClass *oc, void *data)
>      smc->default_caps.caps[SPAPR_CAP_HPT_MAXPAGESIZE] = 16; /* 64kiB
> */
>      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;
>      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 74a48a423a..f03f2f64e7 100644
> --- a/hw/ppc/spapr_caps.c
> +++ b/hw/ppc/spapr_caps.c
> @@ -436,6 +436,21 @@ static void
> cap_large_decr_cpu_apply(sPAPRMachineState *spapr,
>      ppc_store_lpcr(cpu, lpcr);
>  }
>  
> +static void cap_ccf_assist_apply(sPAPRMachineState *spapr, uint8_t
> val,
> +                                 Error **errp)
> +{
> +    uint8_t kvm_val = kvmppc_get_cap_count_cache_flush_assist();
> +
> +    if (tcg_enabled() && val) {
> +        /* TODO - for now only allow broken for TCG */
> +        error_setg(errp,
> +"Requested count cache flush assist capability level not supported
> by tcg, try cap-ccf-assist=off");
> +    } else if (kvm_enabled() && (val > kvm_val)) {
> +        error_setg(errp,
> +"Requested count cache flush assist capability level not supported
> by kvm, try cap-ccf-assist=off");
> +    }

Actually, this should probably be non-fatal if the count cache flush
routine isn't enabled

> +}
> +
>  sPAPRCapabilityInfo capability_table[SPAPR_CAP_NUM] = {
>      [SPAPR_CAP_HTM] = {
>          .name = "htm",
> @@ -525,6 +540,15 @@ sPAPRCapabilityInfo
> capability_table[SPAPR_CAP_NUM] = {
>          .apply = cap_large_decr_apply,
>          .cpu_apply = cap_large_decr_cpu_apply,
>      },
> +    [SPAPR_CAP_CCF_ASSIST] = {
> +        .name = "ccf-assist",
> +        .description = "Count Cache Flush Assist via HW
> Instruction",
> +        .index = SPAPR_CAP_CCF_ASSIST,
> +        .get = spapr_cap_get_bool,
> +        .set = spapr_cap_set_bool,
> +        .type = "bool",
> +        .apply = cap_ccf_assist_apply,
> +    },
>  };
>  
>  static sPAPRCapabilities default_caps_with_cpu(sPAPRMachineState
> *spapr,
> @@ -659,6 +683,7 @@ SPAPR_CAP_MIG_STATE(sbbc, SPAPR_CAP_SBBC);
>  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);
>  
>  void spapr_caps_init(sPAPRMachineState *spapr)
>  {
> diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
> index 4aa8036fc0..8bfdddc964 100644
> --- a/hw/ppc/spapr_hcall.c
> +++ b/hw/ppc/spapr_hcall.c
> @@ -1693,6 +1693,7 @@ static target_ulong
> h_get_cpu_characteristics(PowerPCCPU *cpu,
>      uint8_t safe_cache = spapr_get_cap(spapr, SPAPR_CAP_CFPC);
>      uint8_t safe_bounds_check = spapr_get_cap(spapr,
> SPAPR_CAP_SBBC);
>      uint8_t safe_indirect_branch = spapr_get_cap(spapr,
> SPAPR_CAP_IBS);
> +    uint8_t count_cache_flush_assist = spapr_get_cap(spapr,
> SPAPR_CAP_CCF_ASSIST);
>  
>      switch (safe_cache) {
>      case SPAPR_CAP_WORKAROUND:
> @@ -1733,6 +1734,8 @@ static target_ulong
> h_get_cpu_characteristics(PowerPCCPU *cpu,
>          break;
>      case SPAPR_CAP_WORKAROUND:
>          behaviour |= H_CPU_BEHAV_FLUSH_COUNT_CACHE;
> +        if (count_cache_flush_assist)
> +            characteristics |= H_CPU_CHAR_BCCTR_FLUSH_ASSIST;
>          break;
>      default: /* broken */
>          assert(safe_indirect_branch == SPAPR_CAP_BROKEN);
> diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
> index 80d33ea284..493a44700d 100644
> --- a/include/hw/ppc/spapr.h
> +++ b/include/hw/ppc/spapr.h
> @@ -76,8 +76,10 @@ typedef enum {
>  #define SPAPR_CAP_NESTED_KVM_HV         0x07
>  /* Large Decrementer */
>  #define SPAPR_CAP_LARGE_DECREMENTER     0x08
> +/* Count Cache Flush Assist HW Instruction */
> +#define SPAPR_CAP_CCF_ASSIST            0x09
>  /* Num Caps */
> -#define SPAPR_CAP_NUM                   (SPAPR_CAP_LARGE_DECREMENTER
> + 1)
> +#define SPAPR_CAP_NUM                   (SPAPR_CAP_CCF_ASSIST + 1)
>  
>  /*
>   * Capability Values
> @@ -853,6 +855,7 @@ extern const VMStateDescription
> vmstate_spapr_cap_sbbc;
>  extern const VMStateDescription vmstate_spapr_cap_ibs;
>  extern const VMStateDescription vmstate_spapr_cap_nested_kvm_hv;
>  extern const VMStateDescription vmstate_spapr_cap_large_decr;
> +extern const VMStateDescription vmstate_spapr_cap_ccf_assist;
>  
>  static inline uint8_t spapr_get_cap(sPAPRMachineState *spapr, int
> cap)
>  {
> diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
> index 7a7a5adee3..e0f0de0ce0 100644
> --- a/target/ppc/kvm.c
> +++ b/target/ppc/kvm.c
> @@ -90,6 +90,7 @@ static int cap_ppc_pvr_compat;
>  static int cap_ppc_safe_cache;
>  static int cap_ppc_safe_bounds_check;
>  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;
>  
> @@ -2406,6 +2407,13 @@ static int
> parse_cap_ppc_safe_indirect_branch(struct kvm_ppc_cpu_char c)
>      return 0;
>  }
>  
> +static int parse_cap_ppc_count_cache_flush_assist(struct
> kvm_ppc_cpu_char c)
> +{
> +    if (c.character & c.character_mask &
> H_CPU_CHAR_BCCTR_FLUSH_ASSIST)
> +        return 1;
> +    return 0;
> +}
> +
>  static void kvmppc_get_cpu_characteristics(KVMState *s)
>  {
>      struct kvm_ppc_cpu_char c;
> @@ -2428,6 +2436,7 @@ static void
> kvmppc_get_cpu_characteristics(KVMState *s)
>      cap_ppc_safe_cache = parse_cap_ppc_safe_cache(c);
>      cap_ppc_safe_bounds_check = parse_cap_ppc_safe_bounds_check(c);
>      cap_ppc_safe_indirect_branch =
> parse_cap_ppc_safe_indirect_branch(c);
> +    cap_ppc_count_cache_flush_assist =
> parse_cap_ppc_count_cache_flush_assist(c);
>  }
>  
>  int kvmppc_get_cap_safe_cache(void)
> @@ -2445,6 +2454,11 @@ int kvmppc_get_cap_safe_indirect_branch(void)
>      return cap_ppc_safe_indirect_branch;
>  }
>  
> +int kvmppc_get_cap_count_cache_flush_assist(void)
> +{
> +    return cap_ppc_count_cache_flush_assist;
> +}
> +
>  bool kvmppc_has_cap_nested_kvm_hv(void)
>  {
>      return !!cap_ppc_nested_kvm_hv;
> diff --git a/target/ppc/kvm_ppc.h b/target/ppc/kvm_ppc.h
> index a79835bd14..2937b36cae 100644
> --- a/target/ppc/kvm_ppc.h
> +++ b/target/ppc/kvm_ppc.h
> @@ -62,6 +62,7 @@ bool kvmppc_has_cap_mmu_hash_v3(void);
>  int kvmppc_get_cap_safe_cache(void);
>  int kvmppc_get_cap_safe_bounds_check(void);
>  int kvmppc_get_cap_safe_indirect_branch(void);
> +int kvmppc_get_cap_count_cache_flush_assist(void);
>  bool kvmppc_has_cap_nested_kvm_hv(void);
>  int kvmppc_set_cap_nested_kvm_hv(int enable);
>  int kvmppc_get_cap_large_decr(void);
> @@ -324,6 +325,11 @@ static inline int
> kvmppc_get_cap_safe_indirect_branch(void)
>      return 0;
>  }
>  
> +static inline int kvmppc_get_cap_count_cache_flush_assist(void)
> +{
> +    return 0;
> +}
> +
>  static inline bool kvmppc_has_cap_nested_kvm_hv(void)
>  {
>      return false;