Re: [PATCH v9] target/riscv: Add Smdbltrp ISA extension enable switch

[Daniel Henrique Barboza]

On 1/16/25 10:15 AM, Clément Léger wrote:
> Add the switch to enable the Smdbltrp ISA extension and disable it for
> the max cpu. Indeed, OpenSBI when Smdbltrp is present, M-mode double
> trap is enabled by default and MSTATUS.MDT needs to be cleared to avoid
> taking a double trap. OpenSBI does not currently support it so disable
> it for the max cpu to avoid breaking regression tests.
>
> Signed-off-by: Clément Léger <cleger@rivosinc.com>
> ---

Tested by removing:

drop  0b443cba0d target/riscv: Add Smdbltrp ISA extension enable switch

From riscv-to-apply.next, applying this patch in its place.

'make check-functional' is working again, i.e. there's no problems in
booting the 'max' CPU.


Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>

> Note: this is a resend of patch 9/9 from the double trap series which
> disables this extension for the max cpu. It can be cherry-picked as a
> direct replacement of previous commit.
>
>   target/riscv/cpu.c         |  2 ++
>   target/riscv/tcg/tcg-cpu.c | 10 ++++++++++
>   2 files changed, 12 insertions(+)
>
> diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
> index e3ed11b0fd..bddf1ba75e 100644
> --- a/target/riscv/cpu.c
> +++ b/target/riscv/cpu.c
> @@ -194,6 +194,7 @@ const RISCVIsaExtData isa_edata_arr[] = {
>       ISA_EXT_DATA_ENTRY(smcdeleg, PRIV_VERSION_1_13_0, ext_smcdeleg),
>       ISA_EXT_DATA_ENTRY(smcntrpmf, PRIV_VERSION_1_12_0, ext_smcntrpmf),
>       ISA_EXT_DATA_ENTRY(smcsrind, PRIV_VERSION_1_13_0, ext_smcsrind),
> +    ISA_EXT_DATA_ENTRY(smdbltrp, PRIV_VERSION_1_13_0, ext_smdbltrp),
>       ISA_EXT_DATA_ENTRY(smepmp, PRIV_VERSION_1_12_0, ext_smepmp),
>       ISA_EXT_DATA_ENTRY(smrnmi, PRIV_VERSION_1_12_0, ext_smrnmi),
>       ISA_EXT_DATA_ENTRY(smmpm, PRIV_VERSION_1_13_0, ext_smmpm),
> @@ -1626,6 +1627,7 @@ const RISCVCPUMultiExtConfig riscv_cpu_extensions[] = {
>       MULTI_EXT_CFG_BOOL("ssnpm", ext_ssnpm, false),
>   
>       MULTI_EXT_CFG_BOOL("smaia", ext_smaia, false),
> +    MULTI_EXT_CFG_BOOL("smdbltrp", ext_smdbltrp, false),
>       MULTI_EXT_CFG_BOOL("smepmp", ext_smepmp, false),
>       MULTI_EXT_CFG_BOOL("smrnmi", ext_smrnmi, false),
>       MULTI_EXT_CFG_BOOL("smmpm", ext_smmpm, false),
> diff --git a/target/riscv/tcg/tcg-cpu.c b/target/riscv/tcg/tcg-cpu.c
> index 48be24bbbe..0a137281de 100644
> --- a/target/riscv/tcg/tcg-cpu.c
> +++ b/target/riscv/tcg/tcg-cpu.c
> @@ -1439,6 +1439,16 @@ static void riscv_init_max_cpu_extensions(Object *obj)
>           isa_ext_update_enabled(cpu, CPU_CFG_OFFSET(ext_smrnmi), false);
>           qemu_log("Smrnmi is disabled in the 'max' type CPU\n");
>       }
> +
> +    /*
> +     * ext_smdbltrp requires the firmware to clear MSTATUS.MDT on startup to
> +     * avoid generating a double trap. OpenSBI does not currently support it,
> +     * disable it for now.
> +     */
> +    if (cpu->cfg.ext_smdbltrp) {
> +        isa_ext_update_enabled(cpu, CPU_CFG_OFFSET(ext_smdbltrp), false);
> +        qemu_log("Smdbltrp is disabled in the 'max' type CPU\n");
> +    }
>   }
>   
>   static bool riscv_cpu_has_max_extensions(Object *cpu_obj)