Re: [PATCH v3 3/6] target/riscv: add remaining named features

[Conor Dooley]

On Fri, Feb 02, 2024 at 12:21:51PM -0300, Daniel Henrique Barboza wrote:
> The RVA22U64 and RVA22S64 profiles mandates certain extensions that,
> until now, we were implying that they were available.
> 
> We can't do this anymore since named features also has a riscv,isa
> entry. Let's add them to riscv_cpu_named_features[].
> 
> Instead of adding one bool for each named feature that we'll always
> implement, i.e. can't be turned off, add a 'ext_always_enabled' bool in
> cpu->cfg. This bool will be set to 'true' in TCG accel init, and all
> named features will point to it. This also means that KVM won't see
> these features as always enable, which is our intention.
> 
> If any accelerator adds support to disable one of these features, we'll
> have to promote them to regular extensions and allow users to disable it
> via command line.
> 
> After this patch, here's the riscv,isa from a buildroot using the
> 'rva22s64' CPU:

Why does an "rva22s64" cpu have "zicclsm" in it? Isn't zicclsm only
present in "u" profiles?

>  # cat /proc/device-tree/cpus/cpu@0/riscv,isa
> rv64imafdc_zic64b_zicbom_zicbop_zicboz_ziccamoa_ziccif_zicclsm_ziccrse_
> zicntr_zicsr_zifencei_zihintpause_zihpm_za64rs_zfhmin_zca_zcd_zba_zbb_
> zbs_zkt_ssccptr_sscounterenw_sstvala_sstvecd_svade_svinval_svpbmt#

I want to raise my frustration with the crock we've been given here by
RVI. Any "named feature" that just creates a name for something that
already is assumed is completely useless, and DT property that is used
to communicate it's presence cannot be used - instead the property needs
to be inverted - indicating the absence of that named feature.

Without the inversion, software that parses "riscv,isa" cannot make any
determination based on the absence of the property - it could be parsing
an old DT that does not have the property or it could be parsing the DT
of a system that does not support the extension.

This is part of why I deprecated `riscv,isa`. It's the same problem as
with "zifencei" et al - does a system with `riscv,isa = "rv64imac"`
support fence.i?

Cheers,
Conor.

> 
> Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
> ---
>  target/riscv/cpu.c         | 42 +++++++++++++++++++++++++++++++-------
>  target/riscv/cpu_cfg.h     |  6 ++++++
>  target/riscv/tcg/tcg-cpu.c |  2 ++
>  3 files changed, 43 insertions(+), 7 deletions(-)
> 
> diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
> index 28d3cfa8ce..94843c4f6e 100644
> --- a/target/riscv/cpu.c
> +++ b/target/riscv/cpu.c
> @@ -101,6 +101,10 @@ 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(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),
> @@ -109,6 +113,7 @@ 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(zacas, PRIV_VERSION_1_12_0, ext_zacas),
>      ISA_EXT_DATA_ENTRY(zawrs, PRIV_VERSION_1_12_0, ext_zawrs),
>      ISA_EXT_DATA_ENTRY(zfa, PRIV_VERSION_1_12_0, ext_zfa),
> @@ -170,8 +175,12 @@ 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(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(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(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),
> @@ -1512,6 +1521,11 @@ 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
> @@ -1523,6 +1537,23 @@ const RISCVCPUMultiExtConfig 
> riscv_cpu_named_features[] = {
>      MULTI_EXT_CFG_BOOL("svade", ext_svade, true),
>      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(),
>  };
>  
> @@ -2116,13 +2147,10 @@ static const PropertyInfo prop_marchid = {
>  };
>  
>  /*
> - * RVA22U64 defines some 'named features' or 'synthetic extensions'
> - * that are cache related: Za64rs, Zic64b, Ziccif, Ziccrse, Ziccamoa
> - * and Zicclsm. We do not implement caching in QEMU so we'll consider
> - * all these named features as always enabled.
> - *
> - * There's no riscv,isa update for them (nor for zic64b, despite it
> - * having a cfg offset) at this moment.
> + * RVA22U64 defines some 'named features' that are cache
> + * related: Za64rs, Zic64b, Ziccif, Ziccrse, Ziccamoa
> + * and Zicclsm. They are always implemented in TCG and
> + * doesn't need to be manually enabled by the profile.
>   */
>  static RISCVCPUProfile RVA22U64 = {
>      .parent = NULL,
> diff --git a/target/riscv/cpu_cfg.h b/target/riscv/cpu_cfg.h
> index 698f926ab1..c5049ec664 100644
> --- a/target/riscv/cpu_cfg.h
> +++ b/target/riscv/cpu_cfg.h
> @@ -126,6 +126,12 @@ struct RISCVCPUConfig {
>      bool ext_svade;
>      bool ext_zic64b;
>  
> +    /*
> +     * Always 'true' boolean for named features
> +     * TCG always implement/can't be disabled.
> +     */
> +    bool ext_always_enabled;
> +
>      /* Vendor-specific custom extensions */
>      bool ext_xtheadba;
>      bool ext_xtheadbb;
> diff --git a/target/riscv/tcg/tcg-cpu.c b/target/riscv/tcg/tcg-cpu.c
> index 90861cc065..673097c6e4 100644
> --- a/target/riscv/tcg/tcg-cpu.c
> +++ b/target/riscv/tcg/tcg-cpu.c
> @@ -1347,6 +1347,8 @@ 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);
> -- 
> 2.43.0
> 
>

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