Re: [PATCH for-9.0] target/riscv: do not enable all named features by default

[Alistair Francis]

On Wed, Mar 13, 2024 at 6:33 AM Daniel Henrique Barboza
<dbarboza@ventanamicro.com> wrote:
>
> Commit 3b8022269c added the capability of named features/profile
> extensions to be added in riscv,isa. To do that we had to assign priv
> versions for each one of them in isa_edata_arr[]. But this resulted in a
> side-effect: vendor CPUs that aren't running priv_version_latest started
> to experience warnings for these profile extensions [1]:
>
>   | $ qemu-system-riscv32  -M sifive_e
>   | qemu-system-riscv32: warning: disabling zic64b extension for hart
> 0x00000000 because privilege spec version does not match
>   | qemu-system-riscv32: warning: disabling ziccamoa extension for
> hart 0x00000000 because privilege spec version does not match
>
> This is benign as far as the CPU behavior is concerned since disabling
> both extensions is a no-op (aside from riscv,isa). But the warnings are
> unpleasant to deal with, especially because we're sending user warnings
> for extensions that users can't enable/disable.
>
> Instead of enabling all named features all the time, separate them by
> priv version. During finalize() time, after we decided which
> priv_version the CPU is running, enable/disable all the named extensions
> based on the priv spec chosen. This will be enough for a bug fix, but as
> a future work we should look into how we can name these extensions in a
> way that we don't need an explicit ext_name => priv_ver as we're doing
> here.
>
> The named extensions being added in isa_edata_arr[] that will be
> enabled/disabled based solely on priv version can be removed from
> riscv_cpu_named_features[]. 'zic64b' is an extension that can be
> disabled based on block sizes so it'll retain its own flag and entry.
>
> [1] https://lists.gnu.org/archive/html/qemu-devel/2024-03/msg02592.html
>
> Reported-by: Clément Chigot <chigot@adacore.com>
> Fixes: 3b8022269c ("target/riscv: add riscv,isa to named features")
> Suggested-by: Andrew Jones <ajones@ventanamicro.com>
> Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>

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

Alistair

> ---
>  target/riscv/cpu.c         | 40 +++++++++-----------------------------
>  target/riscv/cpu_cfg.h     |  8 +++++---
>  target/riscv/tcg/tcg-cpu.c | 14 ++++++++++---
>  3 files changed, 25 insertions(+), 37 deletions(-)
>
> diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
> index 5a48d30828..1da5417764 100644
> --- a/target/riscv/cpu.c
> +++ b/target/riscv/cpu.c
> @@ -102,10 +102,10 @@ const RISCVIsaExtData isa_edata_arr[] = {
>      ISA_EXT_DATA_ENTRY(zicbom, PRIV_VERSION_1_12_0, ext_zicbom),
>      ISA_EXT_DATA_ENTRY(zicbop, PRIV_VERSION_1_12_0, ext_zicbop),
>      ISA_EXT_DATA_ENTRY(zicboz, PRIV_VERSION_1_12_0, ext_zicboz),
> -    ISA_EXT_DATA_ENTRY(ziccamoa, PRIV_VERSION_1_11_0, ext_always_enabled),
> -    ISA_EXT_DATA_ENTRY(ziccif, PRIV_VERSION_1_11_0, ext_always_enabled),
> -    ISA_EXT_DATA_ENTRY(zicclsm, PRIV_VERSION_1_11_0, ext_always_enabled),
> -    ISA_EXT_DATA_ENTRY(ziccrse, PRIV_VERSION_1_11_0, ext_always_enabled),
> +    ISA_EXT_DATA_ENTRY(ziccamoa, PRIV_VERSION_1_11_0, has_priv_1_11),
> +    ISA_EXT_DATA_ENTRY(ziccif, PRIV_VERSION_1_11_0, has_priv_1_11),
> +    ISA_EXT_DATA_ENTRY(zicclsm, PRIV_VERSION_1_11_0, has_priv_1_11),
> +    ISA_EXT_DATA_ENTRY(ziccrse, PRIV_VERSION_1_11_0, has_priv_1_11),
>      ISA_EXT_DATA_ENTRY(zicond, PRIV_VERSION_1_12_0, ext_zicond),
>      ISA_EXT_DATA_ENTRY(zicntr, PRIV_VERSION_1_12_0, ext_zicntr),
>      ISA_EXT_DATA_ENTRY(zicsr, PRIV_VERSION_1_10_0, ext_zicsr),
> @@ -114,7 +114,7 @@ const RISCVIsaExtData isa_edata_arr[] = {
>      ISA_EXT_DATA_ENTRY(zihintpause, PRIV_VERSION_1_10_0, ext_zihintpause),
>      ISA_EXT_DATA_ENTRY(zihpm, PRIV_VERSION_1_12_0, ext_zihpm),
>      ISA_EXT_DATA_ENTRY(zmmul, PRIV_VERSION_1_12_0, ext_zmmul),
> -    ISA_EXT_DATA_ENTRY(za64rs, PRIV_VERSION_1_12_0, ext_always_enabled),
> +    ISA_EXT_DATA_ENTRY(za64rs, PRIV_VERSION_1_12_0, has_priv_1_11),
>      ISA_EXT_DATA_ENTRY(zaamo, PRIV_VERSION_1_12_0, ext_zaamo),
>      ISA_EXT_DATA_ENTRY(zacas, PRIV_VERSION_1_12_0, ext_zacas),
>      ISA_EXT_DATA_ENTRY(zalrsc, PRIV_VERSION_1_12_0, ext_zalrsc),
> @@ -179,12 +179,12 @@ const RISCVIsaExtData isa_edata_arr[] = {
>      ISA_EXT_DATA_ENTRY(smepmp, PRIV_VERSION_1_12_0, ext_smepmp),
>      ISA_EXT_DATA_ENTRY(smstateen, PRIV_VERSION_1_12_0, ext_smstateen),
>      ISA_EXT_DATA_ENTRY(ssaia, PRIV_VERSION_1_12_0, ext_ssaia),
> -    ISA_EXT_DATA_ENTRY(ssccptr, PRIV_VERSION_1_11_0, ext_always_enabled),
> +    ISA_EXT_DATA_ENTRY(ssccptr, PRIV_VERSION_1_11_0, has_priv_1_11),
>      ISA_EXT_DATA_ENTRY(sscofpmf, PRIV_VERSION_1_12_0, ext_sscofpmf),
> -    ISA_EXT_DATA_ENTRY(sscounterenw, PRIV_VERSION_1_12_0, 
> ext_always_enabled),
> +    ISA_EXT_DATA_ENTRY(sscounterenw, PRIV_VERSION_1_12_0, has_priv_1_12),
>      ISA_EXT_DATA_ENTRY(sstc, PRIV_VERSION_1_12_0, ext_sstc),
> -    ISA_EXT_DATA_ENTRY(sstvala, PRIV_VERSION_1_12_0, ext_always_enabled),
> -    ISA_EXT_DATA_ENTRY(sstvecd, PRIV_VERSION_1_12_0, ext_always_enabled),
> +    ISA_EXT_DATA_ENTRY(sstvala, PRIV_VERSION_1_12_0, has_priv_1_12),
> +    ISA_EXT_DATA_ENTRY(sstvecd, PRIV_VERSION_1_12_0, has_priv_1_12),
>      ISA_EXT_DATA_ENTRY(svade, PRIV_VERSION_1_11_0, ext_svade),
>      ISA_EXT_DATA_ENTRY(svadu, PRIV_VERSION_1_12_0, ext_svadu),
>      ISA_EXT_DATA_ENTRY(svinval, PRIV_VERSION_1_12_0, ext_svinval),
> @@ -1575,11 +1575,6 @@ const RISCVCPUMultiExtConfig 
> riscv_cpu_experimental_exts[] = {
>      DEFINE_PROP_END_OF_LIST(),
>  };
>
> -#define ALWAYS_ENABLED_FEATURE(_name) \
> -    {.name = _name, \
> -     .offset = CPU_CFG_OFFSET(ext_always_enabled), \
> -     .enabled = true}
> -
>  /*
>   * 'Named features' is the name we give to extensions that we
>   * don't want to expose to users. They are either immutable
> @@ -1590,23 +1585,6 @@ const RISCVCPUMultiExtConfig 
> riscv_cpu_experimental_exts[] = {
>  const RISCVCPUMultiExtConfig riscv_cpu_named_features[] = {
>      MULTI_EXT_CFG_BOOL("zic64b", ext_zic64b, true),
>
> -    /*
> -     * cache-related extensions that are always enabled
> -     * in TCG since QEMU RISC-V does not have a cache
> -     * model.
> -     */
> -    ALWAYS_ENABLED_FEATURE("za64rs"),
> -    ALWAYS_ENABLED_FEATURE("ziccif"),
> -    ALWAYS_ENABLED_FEATURE("ziccrse"),
> -    ALWAYS_ENABLED_FEATURE("ziccamoa"),
> -    ALWAYS_ENABLED_FEATURE("zicclsm"),
> -    ALWAYS_ENABLED_FEATURE("ssccptr"),
> -
> -    /* Other named features that TCG always implements */
> -    ALWAYS_ENABLED_FEATURE("sstvecd"),
> -    ALWAYS_ENABLED_FEATURE("sstvala"),
> -    ALWAYS_ENABLED_FEATURE("sscounterenw"),
> -
>      DEFINE_PROP_END_OF_LIST(),
>  };
>
> diff --git a/target/riscv/cpu_cfg.h b/target/riscv/cpu_cfg.h
> index 2040b90da0..cb750154bd 100644
> --- a/target/riscv/cpu_cfg.h
> +++ b/target/riscv/cpu_cfg.h
> @@ -130,10 +130,12 @@ struct RISCVCPUConfig {
>      bool ext_zic64b;
>
>      /*
> -     * Always 'true' boolean for named features
> -     * TCG always implement/can't be disabled.
> +     * Always 'true' booleans for named features
> +     * TCG always implement/can't be user disabled,
> +     * based on spec version.
>       */
> -    bool ext_always_enabled;
> +    bool has_priv_1_12;
> +    bool has_priv_1_11;
>
>      /* Vendor-specific custom extensions */
>      bool ext_xtheadba;
> diff --git a/target/riscv/tcg/tcg-cpu.c b/target/riscv/tcg/tcg-cpu.c
> index ab6db817db..63192ef54f 100644
> --- a/target/riscv/tcg/tcg-cpu.c
> +++ b/target/riscv/tcg/tcg-cpu.c
> @@ -315,9 +315,19 @@ static void 
> riscv_cpu_disable_priv_spec_isa_exts(RISCVCPU *cpu)
>
>  static void riscv_cpu_update_named_features(RISCVCPU *cpu)
>  {
> +    if (cpu->env.priv_ver >= PRIV_VERSION_1_11_0) {
> +        cpu->cfg.has_priv_1_11 = true;
> +    }
> +
> +    if (cpu->env.priv_ver >= PRIV_VERSION_1_12_0) {
> +        cpu->cfg.has_priv_1_12 = true;
> +    }
> +
> +    /* zic64b is 1.12 or later */
>      cpu->cfg.ext_zic64b = cpu->cfg.cbom_blocksize == 64 &&
>                            cpu->cfg.cbop_blocksize == 64 &&
> -                          cpu->cfg.cboz_blocksize == 64;
> +                          cpu->cfg.cboz_blocksize == 64 &&
> +                          cpu->cfg.has_priv_1_12;
>  }
>
>  static void riscv_cpu_validate_g(RISCVCPU *cpu)
> @@ -1316,8 +1326,6 @@ static void riscv_tcg_cpu_instance_init(CPUState *cs)
>      RISCVCPU *cpu = RISCV_CPU(cs);
>      Object *obj = OBJECT(cpu);
>
> -    cpu->cfg.ext_always_enabled = true;
> -
>      misa_ext_user_opts = g_hash_table_new(NULL, g_direct_equal);
>      multi_ext_user_opts = g_hash_table_new(NULL, g_direct_equal);
>      riscv_cpu_add_user_properties(obj);
> --
> 2.43.2
>
>