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

[Alistair Francis <alistair23@gmail.com>]

On Thu, Feb 1, 2024 at 5:15 AM Daniel Henrique Barboza
<dbarboza@ventanamicro.com> wrote:
>
>
>
> On 1/29/24 22:10, Alistair Francis wrote:
> > On Fri, Jan 26, 2024 at 5:54 AM Daniel Henrique Barboza
> > <dbarboza@ventanamicro.com> 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[].
> >>
> >> They will also need to be explicitly enabled in both profile
> >> descriptions. TCG will enable the named features it already implements,
> >> other accelerators are free to handle it as they like.
> >>
> >> After this patch, here's the riscv,isa from a buildroot using the
> >> 'rva22s64' CPU:
> >>
> >>   # 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_sscounterenw_sstvala_sstvecd_svade_svinval_svpbmt#
> >>
> >> Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
> >> ---
> >>   target/riscv/cpu.c         | 41 +++++++++++++++++++++++++++++---------
> >>   target/riscv/cpu_cfg.h     |  9 +++++++++
> >>   target/riscv/tcg/tcg-cpu.c | 19 +++++++++++++++++-
> >>   3 files changed, 59 insertions(+), 10 deletions(-)
> >>
> >> diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
> >> index 28d3cfa8ce..1ecd8a57ed 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_ziccamoa),
> >> +    ISA_EXT_DATA_ENTRY(ziccif, PRIV_VERSION_1_11_0, ext_ziccif),
> >> +    ISA_EXT_DATA_ENTRY(zicclsm, PRIV_VERSION_1_11_0, ext_zicclsm),
> >> +    ISA_EXT_DATA_ENTRY(ziccrse, PRIV_VERSION_1_11_0, ext_ziccrse),
> >>       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_za64rs),
> >>       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_ssccptr),
> >>       ISA_EXT_DATA_ENTRY(sscofpmf, PRIV_VERSION_1_12_0, ext_sscofpmf),
> >> +    ISA_EXT_DATA_ENTRY(sscounterenw, PRIV_VERSION_1_12_0, ext_sscounterenw),
> >>       ISA_EXT_DATA_ENTRY(sstc, PRIV_VERSION_1_12_0, ext_sstc),
> >> +    ISA_EXT_DATA_ENTRY(sstvala, PRIV_VERSION_1_12_0, ext_sstvala),
> >> +    ISA_EXT_DATA_ENTRY(sstvecd, PRIV_VERSION_1_12_0, ext_sstvecd),
> >>       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),
> >> @@ -1523,6 +1532,22 @@ 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
> >> +     * since QEMU RISC-V does not have a cache model.
> >> +     */
> >> +    MULTI_EXT_CFG_BOOL("za64rs", ext_za64rs, true),
> >> +    MULTI_EXT_CFG_BOOL("ziccif", ext_ziccif, true),
> >> +    MULTI_EXT_CFG_BOOL("ziccrse", ext_ziccrse, true),
> >> +    MULTI_EXT_CFG_BOOL("ziccamoa", ext_ziccamoa, true),
> >> +    MULTI_EXT_CFG_BOOL("zicclsm", ext_zicclsm, true),
> >> +    MULTI_EXT_CFG_BOOL("ssccptr", ext_ssccptr, true),
> >> +
> >> +    /* Other named features that QEMU TCG always implements */
> >> +    MULTI_EXT_CFG_BOOL("sstvecd", ext_sstvecd, true),
> >> +    MULTI_EXT_CFG_BOOL("sstvala", ext_sstvala, true),
> >> +    MULTI_EXT_CFG_BOOL("sscounterenw", ext_sscounterenw, true),
> >> +
> >>       DEFINE_PROP_END_OF_LIST(),
> >>   };
> >>
> >> @@ -2116,13 +2141,8 @@ 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 cache related extensions: Za64rs,
> >> + * Ziccif, Ziccrse, Ziccamoa and Zicclsm.
> >>    */
> >>   static RISCVCPUProfile RVA22U64 = {
> >>       .parent = NULL,
> >> @@ -2139,7 +2159,9 @@ static RISCVCPUProfile RVA22U64 = {
> >>           CPU_CFG_OFFSET(ext_zicbop), CPU_CFG_OFFSET(ext_zicboz),
> >>
> >>           /* mandatory named features for this profile */
> >> -        CPU_CFG_OFFSET(ext_zic64b),
> >> +        CPU_CFG_OFFSET(ext_za64rs), CPU_CFG_OFFSET(ext_zic64b),
> >> +        CPU_CFG_OFFSET(ext_ziccif), CPU_CFG_OFFSET(ext_ziccrse),
> >> +        CPU_CFG_OFFSET(ext_ziccamoa), CPU_CFG_OFFSET(ext_zicclsm),
> >>
> >>           RISCV_PROFILE_EXT_LIST_END
> >>       }
> >> @@ -2170,7 +2192,8 @@ static RISCVCPUProfile RVA22S64 = {
> >>           CPU_CFG_OFFSET(ext_svinval),
> >>
> >>           /* rva22s64 named features */
> >> -        CPU_CFG_OFFSET(ext_svade),
> >> +        CPU_CFG_OFFSET(ext_sstvecd), CPU_CFG_OFFSET(ext_sstvala),
> >> +        CPU_CFG_OFFSET(ext_sscounterenw), CPU_CFG_OFFSET(ext_svade),
> >>
> >>           RISCV_PROFILE_EXT_LIST_END
> >>       }
> >> diff --git a/target/riscv/cpu_cfg.h b/target/riscv/cpu_cfg.h
> >> index 698f926ab1..f79fc3dfd1 100644
> >> --- a/target/riscv/cpu_cfg.h
> >> +++ b/target/riscv/cpu_cfg.h
> >> @@ -125,6 +125,15 @@ struct RISCVCPUConfig {
> >>       /* Named features  */
> >>       bool ext_svade;
> >>       bool ext_zic64b;
> >> +    bool ext_za64rs;
> >> +    bool ext_ziccif;
> >> +    bool ext_ziccrse;
> >> +    bool ext_ziccamoa;
> >> +    bool ext_zicclsm;
> >> +    bool ext_ssccptr;
> >> +    bool ext_sstvecd;
> >> +    bool ext_sstvala;
> >> +    bool ext_sscounterenw;
> >
> > Overall this and the previous patch look fine.
> >
> > One thing though, why store this information? I feel it could be
> > confusing having these variables. If a developer sets them to false
> > nothing actually happens, which is a little misleading
>
> These extensions aren't being exposed to users. riscv_cpu_named_features[] isn't

Yep, we should not expose them to users.

I meant developers, as in people reading the C code and compiling QEMU.

> being used to create any CPU user properties. I should've mentioned that in
> patch 2 ...
>
> As for the extra booleans that we'll be setting to 'true', as it is now
> isa_edata_arr[] stores a string name, priv_ver and a cpu->cfg offset, so
> everyone that adds a riscv,isa str must also have a valid bool offset in
> RISCVCPUConfig. Having a bool also allow us to treat them as regular extensions
> because we can re-use existing code to blindly enable them in profiles like
> any other profile extension.

Yep, and I think that makes sense. The odd part is that we don't
actually use these bools. Which I feel is confusing when looking at
the QEMU code base. Why have a variable that we don't use?

>
> And, in case we need to promote them as regular user extensions, having the
> booleans in place make it easier to do so. Patch 6 is doing that with 'svade'.

If we plan to do that, I think that also makes sense. But I suspect no
one has any plant to convert some of these to real configuration
options.

>
>
> Thanks,
>
> Daniel
>
>
> We could create a single boolean that is always true in cpu->cfg and use it
> for these entries. Another idea would be to change the riscv,isa functions to
> handle these extensions separately, then we can add them in the array without
> a valid cpu->cfg offfset.

I think these are better ideas.

Alistair

>
> >
> > Alistair
> >
> >>
> >>       /* Vendor-specific custom extensions */
> >>       bool ext_xtheadba;
> >> diff --git a/target/riscv/tcg/tcg-cpu.c b/target/riscv/tcg/tcg-cpu.c
> >> index 90861cc065..6d5028cf84 100644
> >> --- a/target/riscv/tcg/tcg-cpu.c
> >> +++ b/target/riscv/tcg/tcg-cpu.c
> >> @@ -206,7 +206,8 @@ static void riscv_cpu_enable_named_feat(RISCVCPU *cpu, uint32_t feat_offset)
> >>           cpu->cfg.ext_svadu = false;
> >>           break;
> >>       default:
> >> -        g_assert_not_reached();
> >> +        /* Named feature already enabled in riscv_tcg_cpu_instance_init */
> >> +        return;
> >>       }
> >>   }
> >>
> >> @@ -1342,6 +1343,20 @@ static bool riscv_cpu_has_max_extensions(Object *cpu_obj)
> >>       return object_dynamic_cast(cpu_obj, TYPE_RISCV_CPU_MAX) != NULL;
> >>   }
> >>
> >> +/* Named features that TCG always implements */
> >> +static void riscv_tcg_cpu_enable_named_feats(RISCVCPU *cpu)
> >> +{
> >> +    cpu->cfg.ext_za64rs = true;
> >> +    cpu->cfg.ext_ziccif = true;
> >> +    cpu->cfg.ext_ziccrse = true;
> >> +    cpu->cfg.ext_ziccamoa = true;
> >> +    cpu->cfg.ext_zicclsm = true;
> >> +    cpu->cfg.ext_ssccptr = true;
> >> +    cpu->cfg.ext_sstvecd = true;
> >> +    cpu->cfg.ext_sstvala = true;
> >> +    cpu->cfg.ext_sscounterenw = true;
> >> +}
> >> +
> >>   static void riscv_tcg_cpu_instance_init(CPUState *cs)
> >>   {
> >>       RISCVCPU *cpu = RISCV_CPU(cs);
> >> @@ -1354,6 +1369,8 @@ static void riscv_tcg_cpu_instance_init(CPUState *cs)
> >>       if (riscv_cpu_has_max_extensions(obj)) {
> >>           riscv_init_max_cpu_extensions(obj);
> >>       }
> >> +
> >> +    riscv_tcg_cpu_enable_named_feats(cpu);
> >>   }
> >>
> >>   static void riscv_tcg_cpu_init_ops(AccelCPUClass *accel_cpu, CPUClass *cc)
> >> --
> >> 2.43.0
> >>
> >>