Re: [PATCH] target/riscv/cpu.c: do not run 'host' CPU with TCG

[Alistair Francis]

On Fri, Jul 21, 2023 at 11:35 PM Daniel Henrique Barboza
<dbarboza@ventanamicro.com> wrote:
>
> The 'host' CPU is available in a CONFIG_KVM build and it's currently
> available for all accels, but is a KVM only CPU. This means that in a
> RISC-V KVM capable host we can do things like this:
>
> $ ./build/qemu-system-riscv64 -M virt,accel=tcg -cpu host --nographic
> qemu-system-riscv64: H extension requires priv spec 1.12.0
>
> This CPU does not have a priv spec because we don't filter its extensions
> via priv spec. We shouldn't be reaching riscv_cpu_realize_tcg() at all
> with the 'host' CPU.
>
> We don't have a way to filter the 'host' CPU out of the available CPU
> options (-cpu help) if the build includes both KVM and TCG. What we can
> do is to error out during riscv_cpu_realize_tcg() if the user chooses
> the 'host' CPU with accel=tcg:
>
> $ ./build/qemu-system-riscv64 -M virt,accel=tcg -cpu host --nographic
> qemu-system-riscv64: 'host' CPU is not compatible with TCG acceleration
>
> Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>

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

Alistair

> ---
>  target/riscv/cpu.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
> index 6b93b04453..08db3d613f 100644
> --- a/target/riscv/cpu.c
> +++ b/target/riscv/cpu.c
> @@ -1395,6 +1395,11 @@ static void riscv_cpu_realize_tcg(DeviceState *dev, 
> Error **errp)
>      CPURISCVState *env = &cpu->env;
>      Error *local_err = NULL;
>
> +    if (object_dynamic_cast(OBJECT(dev), TYPE_RISCV_CPU_HOST)) {
> +        error_setg(errp, "'host' CPU is not compatible with TCG 
> acceleration");
> +        return;
> +    }
> +
>      riscv_cpu_validate_misa_mxl(cpu, &local_err);
>      if (local_err != NULL) {
>          error_propagate(errp, local_err);
> --
> 2.41.0
>
>