Re: [PATCH v9 01/20] target/riscv: skip features setup for KVM CPUs

[Alistair Francis]

On Thu, Jul 6, 2023 at 8:18 PM Daniel Henrique Barboza
<dbarboza@ventanamicro.com> 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:
>
> $ ./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 to 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_tcg() helper contains all validation logic that
> are applicable to TCG CPUs only. riscv_cpu_realize() verifies if we're
> running TCG and, if it's the case, proceed with the usual TCG realize()
> logic.
>
> [1] lib/sbi/sbi_hart.c, hart_detect_features()
>
> Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
> Reviewed-by: Andrew Jones <ajones@ventanamicro.com>

Reviewed-by: Alistair Francis <alistair.francis@wdc.com>

Alistair

> ---
>  target/riscv/cpu.c | 35 +++++++++++++++++++++++++----------
>  1 file changed, 25 insertions(+), 10 deletions(-)
>
> diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
> index fd647534cf..6232e6513b 100644
> --- a/target/riscv/cpu.c
> +++ b/target/riscv/cpu.c
> @@ -34,6 +34,7 @@
>  #include "migration/vmstate.h"
>  #include "fpu/softfloat-helpers.h"
>  #include "sysemu/kvm.h"
> +#include "sysemu/tcg.h"
>  #include "kvm_riscv.h"
>  #include "tcg/tcg.h"
>
> @@ -1386,20 +1387,12 @@ static void 
> riscv_cpu_validate_misa_priv(CPURISCVState *env, Error **errp)
>      }
>  }
>
> -static void riscv_cpu_realize(DeviceState *dev, Error **errp)
> +static void riscv_cpu_realize_tcg(DeviceState *dev, Error **errp)
>  {
> -    CPUState *cs = CPU(dev);
>      RISCVCPU *cpu = RISCV_CPU(dev);
>      CPURISCVState *env = &cpu->env;
> -    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;
> -    }
> -
>      riscv_cpu_validate_misa_mxl(cpu, &local_err);
>      if (local_err != NULL) {
>          error_propagate(errp, local_err);
> @@ -1434,7 +1427,7 @@ static void riscv_cpu_realize(DeviceState *dev, Error 
> **errp)
>      }
>
>  #ifndef CONFIG_USER_ONLY
> -    cs->tcg_cflags |= CF_PCREL;
> +    CPU(dev)->tcg_cflags |= CF_PCREL;
>
>      if (cpu->cfg.ext_sstc) {
>          riscv_timer_init(cpu);
> @@ -1447,6 +1440,28 @@ 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 (tcg_enabled()) {
> +        riscv_cpu_realize_tcg(dev, &local_err);
> +        if (local_err != NULL) {
> +            error_propagate(errp, local_err);
> +            return;
> +        }
> +    }
>
>      riscv_cpu_finalize_features(cpu, &local_err);
>      if (local_err != NULL) {
> --
> 2.41.0
>
>