Re: [Qemu-devel] [PATCH v3 6/6] hw/arm/virt: Support -machine gic-version=max

["Alex Bennée" <alex.bennee@linaro.org>]

Peter Maydell <peter.maydell@linaro.org> writes:

> Add support for passing 'max' to -machine gic-version. By analogy
> with the -cpu max option, this picks the "best available" GIC version
> whether you're using KVM or TCG, so it behaves like 'host' when
> using KVM, and gives you GICv3 when using TCG.
>
> Also like '-cpu host', using -machine gic-version=max' means there
> is no guarantee of migration compatibility between QEMU versions;
> in future 'max' might mean '4'.
>
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
>  hw/arm/virt.c | 29 +++++++++++++++++++----------
>  1 file changed, 19 insertions(+), 10 deletions(-)
>
> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> index cda4b83586..2c07245047 100644
> --- a/hw/arm/virt.c
> +++ b/hw/arm/virt.c
> @@ -1207,16 +1207,23 @@ static void machvirt_init(MachineState *machine)
>      /* We can probe only here because during property set
>       * KVM is not available yet
>       */
> -    if (!vms->gic_version) {
> +    if (vms->gic_version <= 0) {
> +        /* "host" or "max" */
>          if (!kvm_enabled()) {
> -            error_report("gic-version=host requires KVM");
> -            exit(1);
> -        }
> -
> -        vms->gic_version = kvm_arm_vgic_probe();
> -        if (!vms->gic_version) {
> -            error_report("Unable to determine GIC version supported by host");
> -            exit(1);
> +            if (vms->gic_version == 0) {
> +                error_report("gic-version=host requires KVM");
> +                exit(1);
> +            } else {
> +                /* "max": currently means 3 for TCG */
> +                vms->gic_version = 3;
> +            }
> +        } else {
> +            vms->gic_version = kvm_arm_vgic_probe();
> +            if (!vms->gic_version) {
> +                error_report(
> +                    "Unable to determine GIC version supported by host");
> +                exit(1);
> +            }
>          }
>      }
>
> @@ -1480,9 +1487,11 @@ static void virt_set_gic_version(Object *obj, const char *value, Error **errp)
>          vms->gic_version = 2;
>      } else if (!strcmp(value, "host")) {
>          vms->gic_version = 0; /* Will probe later */
> +    } else if (!strcmp(value, "max")) {
> +        vms->gic_version = -1; /* Will probe later */
>      } else {
>          error_setg(errp, "Invalid gic-version value");
> -        error_append_hint(errp, "Valid values are 3, 2, host.\n");
> +        error_append_hint(errp, "Valid values are 3, 2, host,
> max.\n");

nit: host is only valid on aarch64 host. However it will fail later on
with:

  qemu-system-aarch64: gic-version=host requires KVM

Anyway:

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>

--
Alex Bennée