Re: [PATCH v3] target/riscv/kvm: add satp mode for host cpu

[Andrew Jones <ajones@ventanamicro.com>]

On Tue, May 20, 2025 at 06:41:03PM +0800, Meng Zhuo wrote:
> This patch adds host satp mode while kvm/host cpu satp mode is not
> set.
> 
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2931
> Signed-off-by: Meng Zhuo <mengzhuo@iscas.ac.cn>
> ---

Please provide a changelog here. I had to go reread the comments on v1 to
guess at what might have changed.

>  target/riscv/cpu.c         |  3 +--
>  target/riscv/cpu.h         |  1 +
>  target/riscv/kvm/kvm-cpu.c | 20 +++++++++++++++++++-
>  3 files changed, 21 insertions(+), 3 deletions(-)
> 
> diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
> index d92874baa0..a84edd3a3b 100644
> --- a/target/riscv/cpu.c
> +++ b/target/riscv/cpu.c
> @@ -433,8 +433,7 @@ const char *satp_mode_str(uint8_t satp_mode, bool is_32_bit)
>      g_assert_not_reached();
>  }
>  
> -static void set_satp_mode_max_supported(RISCVCPU *cpu,
> -                                        uint8_t satp_mode)
> +void set_satp_mode_max_supported(RISCVCPU *cpu, uint8_t satp_mode)

In v1 I suggested we add some sanity checking to this function to ensure
we can never set an invalid mode (one that's higher than the max
supported).

>  {
>      bool rv32 = riscv_cpu_mxl(&cpu->env) == MXL_RV32;
>      const bool *valid_vm = rv32 ? valid_vm_1_10_32 : valid_vm_1_10_64;
> diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
> index b56d3afa69..d7136f1d72 100644
> --- a/target/riscv/cpu.h
> +++ b/target/riscv/cpu.h
> @@ -915,6 +915,7 @@ char *riscv_cpu_get_name(RISCVCPU *cpu);
>  
>  void riscv_cpu_finalize_features(RISCVCPU *cpu, Error **errp);
>  void riscv_add_satp_mode_properties(Object *obj);
> +void set_satp_mode_max_supported(RISCVCPU *cpu, uint8_t satp_mode);
>  bool riscv_cpu_accelerator_compatible(RISCVCPU *cpu);
>  
>  /* CSR function table */
> diff --git a/target/riscv/kvm/kvm-cpu.c b/target/riscv/kvm/kvm-cpu.c
> index 82f9728636..18fbca1a08 100644
> --- a/target/riscv/kvm/kvm-cpu.c
> +++ b/target/riscv/kvm/kvm-cpu.c
> @@ -999,6 +999,23 @@ static void kvm_riscv_destroy_scratch_vcpu(KVMScratchCPU *scratch)
>      close(scratch->kvmfd);
>  }
>  
> +static void kvm_riscv_init_satp_mode(RISCVCPU *cpu, KVMScratchCPU *kvmcpu)
> +{
> +    CPURISCVState *env = &cpu->env;
> +    struct kvm_one_reg reg;
> +    int ret;
> +    uint64_t val;
> +
> +    reg.id = RISCV_CONFIG_REG(env, satp_mode);
> +    reg.addr = (uint64_t)&val;
> +    ret = ioctl(kvmcpu->cpufd, KVM_GET_ONE_REG, &reg);
> +    if (ret != 0) {
> +        error_report("Unable to retrieve satp from host, error %d", ret);

This will output "Unable..., error -1" on error. We should output at least
the errno and preferably the errno string. I see that this is just a copy
of a pattern used throughout this file though, so we need a patch fixing
all of the ioctl call error_reports.

> +    }
> +
> +    set_satp_mode_max_supported(cpu, val);
> +}
> +
>  static void kvm_riscv_init_machine_ids(RISCVCPU *cpu, KVMScratchCPU *kvmcpu)
>  {
>      struct kvm_one_reg reg;
> @@ -1302,6 +1319,7 @@ static void riscv_init_kvm_registers(Object *cpu_obj)
>      kvm_riscv_init_machine_ids(cpu, &kvmcpu);
>      kvm_riscv_init_misa_ext_mask(cpu, &kvmcpu);
>      kvm_riscv_init_cfg(cpu, &kvmcpu);
> +    kvm_riscv_init_satp_mode(cpu, &kvmcpu);
>  
>      kvm_riscv_destroy_scratch_vcpu(&kvmcpu);
>  }
> @@ -1980,7 +1998,7 @@ static bool kvm_cpu_realize(CPUState *cs, Error **errp)
>          }
>      }
>  
> -   return true;
> +    return true;
>  }
>  
>  void riscv_kvm_cpu_finalize_features(RISCVCPU *cpu, Error **errp)
> -- 
> 2.39.5
> 
>

Otherwise,

Reviewed-by: Andrew Jones <ajones@ventanamicro.com>