Re: [PATCH v5 01/19] target/riscv: skip features setup for KVM CPUs

[Philippe Mathieu-Daudé]

Hi Daniel,

On 27/6/23 18:31, Daniel Henrique Barboza wrote:
> As it is today it's not possible to use '-cpu host' if the RISC-V host
> has RVH enabled. This is the resulting error:
>
> $ sudo ./qemu/build/qemu-system-riscv64 \
>      -machine virt,accel=kvm -m 2G -smp 1 \
>      -nographic -snapshot -kernel ./guest_imgs/Image  \
>      -initrd ./guest_imgs/rootfs_kvm_riscv64.img \
>      -append "earlycon=sbi root=/dev/ram rw" \
>      -cpu host
> qemu-system-riscv64: H extension requires priv spec 1.12.0
>
> This happens because we're checking for priv spec for all CPUs, and
> since we're not setting  env->priv_ver for the 'host' CPU, it's being
> default to zero (i.e. PRIV_SPEC_1_10_0).
>
> In reality env->priv_ver does not make sense when running with the KVM
> 'host' CPU. It's used to gate certain CSRs/extensions during translation
> to make them unavailable if the hart declares an older spec version. It
> doesn't have any other use. E.g. OpenSBI version 1.2 retrieves the spec
> checking if the CSR_MCOUNTEREN, CSR_MCOUNTINHIBIT and CSR_MENVCFG CSRs
> are available [1].
>
> 'priv_ver' is just one example. We're doing a lot of feature validation
> and setup during riscv_cpu_realize() that it doesn't apply KVM CPUs.
> Validating the feature set for those CPUs is a KVM problem that should
> be handled in KVM specific code.
>
> The new riscv_cpu_realize_features() helper contains all validation
> logic that are not applicable to KVM CPUs. riscv_cpu_realize() verifies
> if we're dealing with a KVM CPU and, if not, execute the new helper to
> proceed with the usual realize() logic for all other CPUs.
>
> [1] lib/sbi/sbi_hart.c, hart_detect_features()
>
> Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
> Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
> Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
> ---
>   target/riscv/cpu.c | 43 +++++++++++++++++++++++++++++++++----------
>   1 file changed, 33 insertions(+), 10 deletions(-)
>
> diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
> index fb8458bf74..e515dde208 100644
> --- a/target/riscv/cpu.c
> +++ b/target/riscv/cpu.c
> @@ -331,6 +331,15 @@ static void set_satp_mode_default_map(RISCVCPU *cpu)
>   }
>   #endif
>   
> +static bool riscv_running_kvm(void)
> +{
> +#ifndef CONFIG_USER_ONLY
> +    return kvm_enabled();
> +#else
> +    return false;
> +#endif
> +}

Instead of this, ...

> @@ -1369,6 +1370,28 @@ static void riscv_cpu_realize(DeviceState *dev, Error 
> **errp)
>           }
>        }
>   #endif
> +}
> +
> +static void riscv_cpu_realize(DeviceState *dev, Error **errp)
> +{
> +    CPUState *cs = CPU(dev);
> +    RISCVCPU *cpu = RISCV_CPU(dev);
> +    RISCVCPUClass *mcc = RISCV_CPU_GET_CLASS(dev);
> +    Error *local_err = NULL;
> +
> +    cpu_exec_realizefn(cs, &local_err);
> +    if (local_err != NULL) {
> +        error_propagate(errp, local_err);
> +        return;
> +    }
> +
> +    if (!riscv_running_kvm()) {

... why not simply do:

   #ifndef CONFIG_USER_ONLY

       if (!kvm_enabled()) {

> +        riscv_cpu_realize_features(dev, &local_err);
> +        if (local_err != NULL) {
> +            error_propagate(errp, local_err);
> +            return;
> +        }
> +    }

   #endif

?

If riscv_cpu_realize_features() is for all but KVM, then the
name isn't ideal.