Re: [PATCH v9 14/20] target/riscv/kvm.c: add multi-letter extension KVM properties

[Alistair Francis]

On Thu, Jul 6, 2023 at 8:20 PM Daniel Henrique Barboza
<dbarboza@ventanamicro.com> wrote:
>
> Let's add KVM user properties for the multi-letter extensions that KVM
> currently supports: zicbom, zicboz, zihintpause, zbb, ssaia, sstc,
> svinval and svpbmt.
>
> As with MISA extensions, we're using the KVMCPUConfig type to hold
> information about the state of each extension. However, multi-letter
> extensions have more cases to cover than MISA extensions, so we're
> adding an extra 'supported' flag as well. This flag will reflect if a
> given extension is supported by KVM, i.e. KVM knows how to handle it.
> This is determined during KVM extension discovery in
> kvm_riscv_init_multiext_cfg(), where we test for ENOENT errors. Any
> other error will cause an abort.
>
> The use of the 'user_set' is similar to what we already do with MISA
> extensions: the flag set only if the user is changing the extension
> state.
>
> The 'supported' flag will be used later on to make an exception for
> users that are disabling multi-letter extensions that are unknown to
> KVM.
>
> Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>

Acked-by: Alistair Francis <alistair.francis@wdc.com>

Alistair

> ---
>  target/riscv/cpu.c |   8 +++
>  target/riscv/kvm.c | 119 +++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 127 insertions(+)
>
> diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
> index 5c8832a030..31e591a938 100644
> --- a/target/riscv/cpu.c
> +++ b/target/riscv/cpu.c
> @@ -1860,6 +1860,14 @@ static void riscv_cpu_add_user_properties(Object *obj)
>      riscv_cpu_add_misa_properties(obj);
>
>      for (prop = riscv_cpu_extensions; prop && prop->name; prop++) {
> +#ifndef CONFIG_USER_ONLY
> +        if (kvm_enabled()) {
> +            /* Check if KVM created the property already */
> +            if (object_property_find(obj, prop->name)) {
> +                continue;
> +            }
> +        }
> +#endif
>          qdev_property_add_static(dev, prop);
>      }
>
> diff --git a/target/riscv/kvm.c b/target/riscv/kvm.c
> index 7afd6024e6..2d39ec154f 100644
> --- a/target/riscv/kvm.c
> +++ b/target/riscv/kvm.c
> @@ -113,6 +113,7 @@ typedef struct KVMCPUConfig {
>      target_ulong offset;
>      int kvm_reg_id;
>      bool user_set;
> +    bool supported;
>  } KVMCPUConfig;
>
>  #define KVM_MISA_CFG(_bit, _reg_id) \
> @@ -197,6 +198,81 @@ static void kvm_riscv_update_cpu_misa_ext(RISCVCPU *cpu, 
> CPUState *cs)
>      }
>  }
>
> +#define CPUCFG(_prop) offsetof(struct RISCVCPUConfig, _prop)
> +
> +#define KVM_EXT_CFG(_name, _prop, _reg_id) \
> +    {.name = _name, .offset = CPUCFG(_prop), \
> +     .kvm_reg_id = _reg_id}
> +
> +static KVMCPUConfig kvm_multi_ext_cfgs[] = {
> +    KVM_EXT_CFG("zicbom", ext_icbom, KVM_RISCV_ISA_EXT_ZICBOM),
> +    KVM_EXT_CFG("zicboz", ext_icboz, KVM_RISCV_ISA_EXT_ZICBOZ),
> +    KVM_EXT_CFG("zihintpause", ext_zihintpause, 
> KVM_RISCV_ISA_EXT_ZIHINTPAUSE),
> +    KVM_EXT_CFG("zbb", ext_zbb, KVM_RISCV_ISA_EXT_ZBB),
> +    KVM_EXT_CFG("ssaia", ext_ssaia, KVM_RISCV_ISA_EXT_SSAIA),
> +    KVM_EXT_CFG("sstc", ext_sstc, KVM_RISCV_ISA_EXT_SSTC),
> +    KVM_EXT_CFG("svinval", ext_svinval, KVM_RISCV_ISA_EXT_SVINVAL),
> +    KVM_EXT_CFG("svpbmt", ext_svpbmt, KVM_RISCV_ISA_EXT_SVPBMT),
> +};
> +
> +static void kvm_cpu_cfg_set(RISCVCPU *cpu, KVMCPUConfig *multi_ext,
> +                            uint32_t val)
> +{
> +    int cpu_cfg_offset = multi_ext->offset;
> +    bool *ext_enabled = (void *)&cpu->cfg + cpu_cfg_offset;
> +
> +    *ext_enabled = val;
> +}
> +
> +static uint32_t kvm_cpu_cfg_get(RISCVCPU *cpu,
> +                                KVMCPUConfig *multi_ext)
> +{
> +    int cpu_cfg_offset = multi_ext->offset;
> +    bool *ext_enabled = (void *)&cpu->cfg + cpu_cfg_offset;
> +
> +    return *ext_enabled;
> +}
> +
> +static void kvm_cpu_set_multi_ext_cfg(Object *obj, Visitor *v,
> +                                      const char *name,
> +                                      void *opaque, Error **errp)
> +{
> +    KVMCPUConfig *multi_ext_cfg = opaque;
> +    RISCVCPU *cpu = RISCV_CPU(obj);
> +    bool value, host_val;
> +
> +    if (!visit_type_bool(v, name, &value, errp)) {
> +        return;
> +    }
> +
> +    host_val = kvm_cpu_cfg_get(cpu, multi_ext_cfg);
> +
> +    /*
> +     * Ignore if the user is setting the same value
> +     * as the host.
> +     */
> +    if (value == host_val) {
> +        return;
> +    }
> +
> +    if (!multi_ext_cfg->supported) {
> +        /*
> +         * Error out if the user is trying to enable an
> +         * extension that KVM doesn't support. Ignore
> +         * option otherwise.
> +         */
> +        if (value) {
> +            error_setg(errp, "KVM does not support disabling extension %s",
> +                       multi_ext_cfg->name);
> +        }
> +
> +        return;
> +    }
> +
> +    multi_ext_cfg->user_set = true;
> +    kvm_cpu_cfg_set(cpu, multi_ext_cfg, value);
> +}
> +
>  static void kvm_riscv_add_cpu_user_properties(Object *cpu_obj)
>  {
>      int i;
> @@ -215,6 +291,15 @@ static void kvm_riscv_add_cpu_user_properties(Object 
> *cpu_obj)
>          object_property_set_description(cpu_obj, misa_cfg->name,
>                                          misa_cfg->description);
>      }
> +
> +    for (i = 0; i < ARRAY_SIZE(kvm_multi_ext_cfgs); i++) {
> +        KVMCPUConfig *multi_cfg = &kvm_multi_ext_cfgs[i];
> +
> +        object_property_add(cpu_obj, multi_cfg->name, "bool",
> +                            NULL,
> +                            kvm_cpu_set_multi_ext_cfg,
> +                            NULL, multi_cfg);
> +    }
>  }
>
>  static int kvm_riscv_get_regs_core(CPUState *cs)
> @@ -530,6 +615,39 @@ static void kvm_riscv_init_misa_ext_mask(RISCVCPU *cpu,
>      env->misa_ext = env->misa_ext_mask;
>  }
>
> +static void kvm_riscv_init_multiext_cfg(RISCVCPU *cpu, KVMScratchCPU *kvmcpu)
> +{
> +    CPURISCVState *env = &cpu->env;
> +    uint64_t val;
> +    int i, ret;
> +
> +    for (i = 0; i < ARRAY_SIZE(kvm_multi_ext_cfgs); i++) {
> +        KVMCPUConfig *multi_ext_cfg = &kvm_multi_ext_cfgs[i];
> +        struct kvm_one_reg reg;
> +
> +        reg.id = kvm_riscv_reg_id(env, KVM_REG_RISCV_ISA_EXT,
> +                                  multi_ext_cfg->kvm_reg_id);
> +        reg.addr = (uint64_t)&val;
> +        ret = ioctl(kvmcpu->cpufd, KVM_GET_ONE_REG, &reg);
> +        if (ret != 0) {
> +            if (errno == EINVAL) {
> +                /* Silently default to 'false' if KVM does not support it. */
> +                multi_ext_cfg->supported = false;
> +                val = false;
> +            } else {
> +                error_report("Unable to read ISA_EXT KVM register %s, "
> +                             "error %d", multi_ext_cfg->name, ret);
> +                kvm_riscv_destroy_scratch_vcpu(kvmcpu);
> +                exit(EXIT_FAILURE);
> +            }
> +        } else {
> +            multi_ext_cfg->supported = true;
> +        }
> +
> +        kvm_cpu_cfg_set(cpu, multi_ext_cfg, val);
> +    }
> +}
> +
>  void kvm_riscv_init_user_properties(Object *cpu_obj)
>  {
>      RISCVCPU *cpu = RISCV_CPU(cpu_obj);
> @@ -542,6 +660,7 @@ void kvm_riscv_init_user_properties(Object *cpu_obj)
>      kvm_riscv_add_cpu_user_properties(cpu_obj);
>      kvm_riscv_init_machine_ids(cpu, &kvmcpu);
>      kvm_riscv_init_misa_ext_mask(cpu, &kvmcpu);
> +    kvm_riscv_init_multiext_cfg(cpu, &kvmcpu);
>
>      kvm_riscv_destroy_scratch_vcpu(&kvmcpu);
>  }
> --
> 2.41.0
>
>