Re: [PATCH 1/7] riscv: implement Ssqosid extension and srmcfg CSR

["Radim Krčmář" <rkrcmar@ventanamicro.com>]

2025-11-19T16:42:17-08:00, Drew Fustini <fustini@kernel.org>:
> From: Kornel Dulęba <mindal@semihalf.com>
>
> Implement the srmcfg CSR defined by the Ssqosid ISA extension
> (Supervisor-mode Quality of Service ID). The CSR contains two fields:
>
>   - Resource Control ID (RCID) used determine resource allocation
>   - Monitoring Counter ID (MCID) used to track resource usage
>
> The CSR is defined for S-mode but accessing it when V=1 shall cause a
> virtual instruction exception. Implement this behavior by calling the
> hmode predicate.
>
> Link: https://github.com/riscv-non-isa/riscv-cbqri/releases/download/v1.0/riscv-cbqri.pdf
> Signed-off-by: Kornel Dulęba <mindal@semihalf.com>
> [fustini: rebase on v10.1.50, fix check_srmcfg]
> Signed-off-by: Drew Fustini <fustini@kernel.org>
> ---
> diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
> @@ -216,6 +216,7 @@ const RISCVIsaExtData isa_edata_arr[] = {
>      ISA_EXT_DATA_ENTRY(ssdbltrp, PRIV_VERSION_1_13_0, ext_ssdbltrp),
>      ISA_EXT_DATA_ENTRY(ssnpm, PRIV_VERSION_1_13_0, ext_ssnpm),
>      ISA_EXT_DATA_ENTRY(sspm, PRIV_VERSION_1_13_0, ext_sspm),
> +    ISA_EXT_DATA_ENTRY(ssqosid, PRIV_VERSION_1_12_0, ext_ssqosid),

Just out of curiosity, where does PRIV_VERSION_1_12_0 come from?

> diff --git a/target/riscv/csr.c b/target/riscv/csr.c
> @@ -1759,6 +1759,37 @@ static RISCVException write_stimecmph(CPURISCVState *env, int csrno,
> +static RISCVException check_srmcfg(CPURISCVState *env, int csrno)
> +{
> +    RISCVCPU *cpu = env_archcpu(env);
> +
> +    if (!cpu->cfg.ext_ssqosid) {
> +        return RISCV_EXCP_ILLEGAL_INST;
> +    }
> +
> +    /*
> +     * Even though this is an S-mode CSR the spec says that we need to throw
> +     * and virt instruction fault if a guest tries to access it.
> +     */
> +    return env->virt_enabled ?
> +           RISCV_EXCP_VIRT_INSTRUCTION_FAULT : smode(env, csrno);
> +}

The check is missing interaction with mstateen0.SRMCFG.

Thanks.