Re: [PATCH v4 3/6] tools/arm: choose GIC version explicitly instead of relying on GIC_NATIVE

On 20-Aug-26 14:40, Julian Vetter wrote:
> XEN_DOMCTL_CONFIG_GIC_NATIVE lets the toolstack ask Xen to silently
> resolve the domain's GIC version to whatever the host hardware has. Xen
> then writes the resolved value back into the same in/out
> xen_arch_domainconfig the toolstack used as input, which is the kind of
> API abuse we're trying to get rid of. The struct passed to createdomain
> should only be an input parameter.
> 
> Move the "pick the best available GIC version" decision to the
> toolstack, using the XEN_SYSCTL_PHYSCAP_ARM_GIC_V2/V3 capability bits
> already exposed via XEN_SYSCTL_physinfo:
> 
>  * libxl__arch_domain_build_info_setdefault() resolves
>    LIBXL_GIC_VERSION_DEFAULT to v3 if available, else v2, else fails,
`LIBXL_GIC_VERSION_DEFAULT` should be renamed to `LIBXL_GIC_VERSION_NONE` to
denote that the user did not set any particular version. With your change there
is no default and `libxl__arch_domain_build_info_setdefault()` resolves it
before anything else can see it.

>    before the config is built.
>  * The Python xc.domain_create() binding does the same via a call to
>    xc_physinfo().
>  * libxl__arch_domain_prepare_config() therefore only ever sees a
>    concrete v2/v3 request and just validates it. The GIC_NATIVE case is
>    dropped since setdefault() always resolves it first.
> 
> This guarantees no toolstack path can still produce
> XEN_DOMCTL_CONFIG_GIC_NATIVE, in preparation for removing it from the
> Xen side and from the ABI entirely.
> 
> Signed-off-by: Julian Vetter <[email protected]>
> ---
> Changes in v4:
> - Fix a missing closing bracket in arch_capabilities_arm_has()
> ---
>  .../include/xen-tools/arm-arch-capabilities.h | 17 ++++++++++++++++
>  tools/libs/light/libxl_arm.c                  | 17 +++++++++++++---
>  tools/python/xen/lowlevel/xc/xc.c             | 20 ++++++++++++++++++-
You need to update the documentation (i.e. xl.cfg) too.

>  3 files changed, 50 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/include/xen-tools/arm-arch-capabilities.h b/tools/include/xen-tools/arm-arch-capabilities.h
> index 4aa4c6c34a..ce1b3bdd71 100644
> --- a/tools/include/xen-tools/arm-arch-capabilities.h
> +++ b/tools/include/xen-tools/arm-arch-capabilities.h
> @@ -6,6 +6,7 @@
>  #ifndef ARM_ARCH_CAPABILITIES_H
>  #define ARM_ARCH_CAPABILITIES_H
>  
> +#include <stdbool.h>
>  #include <stdint.h>
>  #include <xen/sysctl.h>
>  
> @@ -25,4 +26,20 @@ unsigned int arch_capabilities_arm_sve(unsigned int arch_capabilities)
>  #endif
>  }
>  
> +/*
> + * Generic test for any single-bit XEN_SYSCTL_PHYSCAP_ARM_* capability, e.g.
What makes the implementation single-bit?

Otherwise, LGTM.

~Michal