Re: [PATCH v3 4/6] xen/arm: remove XEN_DOMCTL_CONFIG_GIC_NATIVE from the ABI

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 16/07/2026 3:11 pm, Julian Vetter wrote:
> Now that the toolstack always resolves a concrete GIC_V2 or GIC_V3
> before calling createdomain, nothing on the Xen side needs to resolve
> GIC_NATIVE either:
>
>  * A new gic_domctl_version() helper returns the XEN_DOMCTL_CONFIG_GIC_*
>    value matching the host's gic_hw_version().
>  * arch_sanitise_domain_config() uses it to validate that the requested
>    version is compatible with the hardware, rather than resolving
>    GIC_NATIVE and writing the result back into config->arch.gic_version.
>    There's currently no support to run a guest on a GIC version other
>    than the host's, so this is just an equality check.
>  * create_dom0() and arch_parse_dom0less_node(), which both always want
>    a vGIC that exactly matches the hardware, use the same helper instead
>    of GIC_NATIVE.
>
> With nothing left resolving or relying on it, drop
> XEN_DOMCTL_CONFIG_GIC_NATIVE from the public ABI. Every caller must now
> request a concrete GIC_V2 or GIC_V3.
>
> This is an incompatible change for any toolstack still passing 0
> (formerly GIC_NATIVE) expecting Xen to auto-select a version, so bump
> XEN_DOMCTL_INTERFACE_VERSION and add a CHANGELOG.md entry.

This is an API change, not an ABI change, so you can leave the
XEN_DOMCTL_INTERFACE_VERSION alone.

>
> Signed-off-by: Julian Vetter <julian.vetter@vates.tech>
> ---
> Changes in v3:
> - Second half of previous patch 3, with only the changes to Xen
> ---
>  CHANGELOG.md                   |  3 +++
>  xen/arch/arm/dom0less-build.c  |  3 ++-
>  xen/arch/arm/domain.c          | 25 +++++++++----------------
>  xen/arch/arm/domain_build.c    |  3 ++-
>  xen/arch/arm/gic.c             | 16 ++++++++++++++++
>  xen/arch/arm/include/asm/gic.h |  6 ++++++
>  xen/include/public/arch-arm.h  |  1 -
>  xen/include/public/domctl.h    |  4 ++--
>  8 files changed, 40 insertions(+), 21 deletions(-)
>
> diff --git a/CHANGELOG.md b/CHANGELOG.md
> index 356be88351..74f02e91db 100644
> --- a/CHANGELOG.md
> +++ b/CHANGELOG.md
> @@ -13,6 +13,9 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
>  ### Added
>  
>  ### Removed
> + - On Arm:
> +   - XEN_DOMCTL_CONFIG_GIC_NATIVE has been removed.  Toolstacks must now
> +     explicitly request GIC_V2 or GIC_V3 when creating a domain.

"Available GIC versions can be queried via XEN_SYSCTL_physinfo."

> diff --git a/xen/arch/arm/domain.c b/xen/arch/arm/domain.c
> index baa3a5d708..b396d5e615 100644
> --- a/xen/arch/arm/domain.c
> +++ b/xen/arch/arm/domain.c
> @@ -609,23 +609,16 @@ int arch_sanitise_domain_config(struct xen_domctl_createdomain *config)
>          return -EINVAL;
>      }
>  
> -    /* Fill in the native GIC version, passed back to the toolstack. */
> -    if ( config->arch.gic_version == XEN_DOMCTL_CONFIG_GIC_NATIVE )
> +    /*
> +     * The toolstack must pick a specific GIC version. Xen doesn't choose on
> +     * its behalf. It only checks the requested version matches what the
> +     * hardware actually has. There's currently no support to run a guest on a
> +     * GIC version other than the host's.

This is path is used by Xen too, so "toolstack" isn't right. 

Really, this only wants to be the final sentence.  Everything else is
trivially clear from the following logic.

> +     */
> +    if ( config->arch.gic_version != gic_domctl_version() )
>      {
> -        switch ( gic_hw_version() )
> -        {
> -        case GIC_V2:
> -            config->arch.gic_version = XEN_DOMCTL_CONFIG_GIC_V2;
> -            break;
> -
> -        case GIC_V3:
> -            config->arch.gic_version = XEN_DOMCTL_CONFIG_GIC_V3;
> -            break;
> -
> -        default:
> -            ASSERT_UNREACHABLE();
> -            return -EINVAL;
> -        }
> +        dprintk(XENLOG_INFO, "Unsupported GIC version\n");

"Unsupported GIC version %d\n"

When complaining that a value is wrong, state what it is.  That's far
more useful than "something went wrong".  In particular, finding 0 in
this error message means that some caller hasn't been updated to avoid
passing NATIVE.

> diff --git a/xen/include/public/arch-arm.h b/xen/include/public/arch-arm.h
> index 7d6f87e8b2..6987f5bdf4 100644
> --- a/xen/include/public/arch-arm.h
> +++ b/xen/include/public/arch-arm.h
> @@ -319,7 +319,6 @@ DEFINE_XEN_GUEST_HANDLE(vcpu_guest_context_t);
>   * struct xen_arch_domainconfig's ABI is covered by
>   * XEN_DOMCTL_INTERFACE_VERSION.
>   */
> -#define XEN_DOMCTL_CONFIG_GIC_NATIVE    0

We tend leave bredcrumbs around when removing constants.

/*      XEN_DOMCTL_CONFIG_GIC_NATIVE    1 - removed in Xen 4.23 */

~Andrew