On Tue, May 19, 2026 at 08:48:58AM +0800, Daniel Henrique Barboza wrote:
> Priv spec chapter "Svpbmt Extension for Page-Based Memory Types, Version
> 1.0" mentions that "The Svpbmt extension depends on the Sv39
> extension.".
>
> We're not doing any satp checks when enabling svpbmt. This causes
> problems with the riscv32 'max' CPU that happens to be enabling svpbmt
> even though it doesn't support the required satp mode. In fact all rv32
> CPUs are allowing menvcfg.PBMTE writes, which doesn't make sense for
> them in any circunstance since svpbmt is not possible for rv32 at this
> moment [1].
>
> This also impacts rv64 CPUs that are running in satp 'bare' mode and are
> reporting svpbmt in the riscv,isa.
>
> All these problems can be solved by disabling svpbmt if satp_mode is not
> at least sv39. The problem reported in [1] goes away because we'll
> never enable MENVCFG_PBMTE write mask in write_menvcfgh(). We're also
> become consistent with how svpbmt is enabled for rv64.
>
> In case the user enables svpbmt in the command line using an invalid setup,
> not just disable svpbmt but also throw a warning:
>
> $ ./build/qemu-system-riscv64 -M virt,dumpdtb=fdt.dtb \
> -cpu max,sv39=off,sv48=off,sv57=off,sv64=off,svpbmt=on
> qemu-system-riscv64: warning: svpbmt requires at least satp sv39, current
> satp mode: none
>
> [1] https://gitlab.com/qemu-project/qemu/-/work_items/3473
>
> Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/3473
> Signed-off-by: Daniel Henrique Barboza <[email protected]>
Reviewed-by: Chao Liu <[email protected]>
> ---
> target/riscv/tcg/tcg-cpu.c | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff --git a/target/riscv/tcg/tcg-cpu.c b/target/riscv/tcg/tcg-cpu.c
> index a358d91ca5..5b3e36d9ab 100644
> --- a/target/riscv/tcg/tcg-cpu.c
> +++ b/target/riscv/tcg/tcg-cpu.c
> @@ -887,6 +887,17 @@ void riscv_cpu_validate_set_extensions(RISCVCPU *cpu,
> Error **errp)
> return;
> }
>
> +#ifndef CONFIG_USER_ONLY
> + if (cpu->cfg.ext_svpbmt && cpu->cfg.max_satp_mode < VM_1_10_SV39) {
> + cpu->cfg.ext_svpbmt = false;
> + if (cpu_cfg_ext_is_user_set(CPU_CFG_OFFSET(ext_svpbmt))) {
> + warn_report("svpbmt requires at least satp sv39, "
> + "current satp mode: %s",
> + satp_mode_str(cpu->cfg.max_satp_mode,
> + riscv_cpu_is_32bit(cpu)));
> + }
> + }
> +#endif
> /*
> * Disable isa extensions based on priv spec after we
> * validated and set everything we need.
> --
> 2.43.0
>
