[PATCH v5 3/6] tools/arm: choose GIC version explicitly instead of relying on GIC_NATIVE

[Julian Vetter <julian.vetter@xxxxxxxxxx>]

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 the GIC version
   against those bits before the config is built. An unspecified version
   becomes v3 if available, else v2, else fails. An explicitly requested
   v2/v3 is validated against the same bits, so a version the host
   cannot provide is directly rejected in the toolstack.
 * 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.

The LIBXL_GIC_VERSION enum value 0 is renamed from DEFAULT to NONE to
reflect that it now only means "the user did not pick a version".
setdefault() resolves it before anything else can observe it, so there
is no longer a "default" left in the config. The xl.cfg(5) gic_version
documentation is updated to match.

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 <julian.vetter@xxxxxxxxxx>
---
Changes in v5:
- Go back to the initial per-version arch_capabilities_arm_gic_{v2,v3}()
  helpers instead of a generic arch_capabilities_arm_has(caps, mask)
- Validate an explicitly requested GIC version against the host
  capabilities, not just resolve an unspecified one
- Rename LIBXL_GIC_VERSION_DEFAULT to LIBXL_GIC_VERSION_NONE
- Document the change in xl.cfg(5)
---
 docs/man/xl.cfg.5.pod.in                      |  9 ++--
 .../include/xen-tools/arm-arch-capabilities.h | 21 +++++++++
 tools/libs/light/libxl_arm.c                  | 45 +++++++++++++++++--
 tools/libs/light/libxl_types.idl              |  4 +-
 tools/python/xen/lowlevel/xc/xc.c             | 18 +++++++-
 5 files changed, 87 insertions(+), 10 deletions(-)

diff --git a/docs/man/xl.cfg.5.pod.in b/docs/man/xl.cfg.5.pod.in
index d34951edb9..6a5e75eeab 100644
--- a/docs/man/xl.cfg.5.pod.in
+++ b/docs/man/xl.cfg.5.pod.in
@@ -3081,15 +3081,16 @@ Emulate a GICv2
 Emulate a GICv3. Note that the emulated GIC does not support the
 GICv2 compatibility mode.
 
-=item B<default>
+=item B<none>
 
-Emulate the same version as the native GIC hardware used by the host where
-the domain was created.
+Let the toolstack choose the GIC version: GICv3 if the host supports it,
+otherwise GICv2. This is the default when C<gic_version> is not specified.
 
 =back
 
 This requires hardware compatibility with the requested version, either
-natively or via hardware backwards compatibility support.
+natively or via hardware backwards compatibility support. The GIC versions
+the host can emulate for a guest are reported via C<XEN_SYSCTL_physinfo>.
 
 =item B<vuart="uart">
 
diff --git a/tools/include/xen-tools/arm-arch-capabilities.h 
b/tools/include/xen-tools/arm-arch-capabilities.h
index 4aa4c6c34a..21e3c73bd1 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 +26,24 @@ unsigned int arch_capabilities_arm_sve(unsigned int 
arch_capabilities)
 #endif
 }
 
+static inline
+bool arch_capabilities_arm_gic_v2(unsigned int arch_capabilities)
+{
+#if defined(__arm__) || defined(__aarch64__)
+    return MASK_EXTR(arch_capabilities, XEN_SYSCTL_PHYSCAP_ARM_GIC_V2);
+#else
+    return false;
+#endif
+}
+
+static inline
+bool arch_capabilities_arm_gic_v3(unsigned int arch_capabilities)
+{
+#if defined(__arm__) || defined(__aarch64__)
+    return MASK_EXTR(arch_capabilities, XEN_SYSCTL_PHYSCAP_ARM_GIC_V3);
+#else
+    return false;
+#endif
+}
+
 #endif /* ARM_ARCH_CAPABILITIES_H */
diff --git a/tools/libs/light/libxl_arm.c b/tools/libs/light/libxl_arm.c
index 7e9f8a1bc3..283cfb749b 100644
--- a/tools/libs/light/libxl_arm.c
+++ b/tools/libs/light/libxl_arm.c
@@ -196,9 +196,6 @@ int libxl__arch_domain_prepare_config(libxl__gc *gc,
     LOG(DEBUG, " - Allocate %u SPIs", config->arch.nr_spis);
 
     switch (d_config->b_info.arch_arm.gic_version) {
-    case LIBXL_GIC_VERSION_DEFAULT:
-        config->arch.gic_version = XEN_DOMCTL_CONFIG_GIC_NATIVE;
-        break;
     case LIBXL_GIC_VERSION_V2:
         config->arch.gic_version = XEN_DOMCTL_CONFIG_GIC_V2;
         break;
@@ -1800,6 +1797,48 @@ int libxl__arch_domain_build_info_setdefault(libxl__gc 
*gc,
     /* Trapping of unmapped accesses enabled by default.  */
     libxl_defbool_setdefault(&b_info->trap_unmapped_accesses, true);
 
+    /*
+     * Resolve the GIC version against the host capabilities reported by
+     * XEN_SYSCTL_physinfo. If the user didn't request a specific version, pick
+     * the best one available. Otherwise validate the requested version here,
+     * so a bad request fails early instead of in the hypervisor.
+     */
+    {
+        bool has_v3 = 
arch_capabilities_arm_gic_v3(physinfo->arch_capabilities);
+        bool has_v2 = 
arch_capabilities_arm_gic_v2(physinfo->arch_capabilities);
+
+        switch (b_info->arch_arm.gic_version) {
+        case LIBXL_GIC_VERSION_NONE:
+            if (has_v3)
+                b_info->arch_arm.gic_version = LIBXL_GIC_VERSION_V3;
+            else if (has_v2)
+                b_info->arch_arm.gic_version = LIBXL_GIC_VERSION_V2;
+            else {
+                LOG(ERROR, "No supported GIC version found on this host");
+                return ERROR_FAIL;
+            }
+            break;
+
+        case LIBXL_GIC_VERSION_V3:
+            if (!has_v3) {
+                LOG(ERROR, "GICv3 requested but not supported on this host");
+                return ERROR_FAIL;
+            }
+            break;
+
+        case LIBXL_GIC_VERSION_V2:
+            if (!has_v2) {
+                LOG(ERROR, "GICv2 requested but not supported on this host");
+                return ERROR_FAIL;
+            }
+            break;
+
+        default:
+            LOG(ERROR, "Unknown GIC version %d", b_info->arch_arm.gic_version);
+            return ERROR_FAIL;
+        }
+    }
+
     /* Sanitise SVE parameter */
     if (b_info->arch_arm.sve_vl) {
         unsigned int max_sve_vl =
diff --git a/tools/libs/light/libxl_types.idl b/tools/libs/light/libxl_types.idl
index a7893460f0..8699ab3013 100644
--- a/tools/libs/light/libxl_types.idl
+++ b/tools/libs/light/libxl_types.idl
@@ -520,10 +520,10 @@ libxl_vnode_info = Struct("vnode_info", [
     ])
 
 libxl_gic_version = Enumeration("gic_version", [
-    (0, "DEFAULT"),
+    (0, "NONE"),
     (0x20, "v2"),
     (0x30, "v3")
-    ], init_val = "LIBXL_GIC_VERSION_DEFAULT")
+    ], init_val = "LIBXL_GIC_VERSION_NONE")
 
 libxl_tee_type = Enumeration("tee_type", [
     (0, "none"),
diff --git a/tools/python/xen/lowlevel/xc/xc.c 
b/tools/python/xen/lowlevel/xc/xc.c
index 7a4bf54597..0127b4b1b7 100644
--- a/tools/python/xen/lowlevel/xc/xc.c
+++ b/tools/python/xen/lowlevel/xc/xc.c
@@ -163,7 +163,23 @@ static PyObject *pyxc_domain_create(XcObject *self,
                                       ~(XEN_X86_EMU_VPCI |
                                         XEN_X86_EMU_USE_PIRQ);
 #elif defined (__arm__) || defined(__aarch64__)
-    config.arch.gic_version = XEN_DOMCTL_CONFIG_GIC_NATIVE;
+    {
+        xc_physinfo_t pinfo;
+
+        if ( xc_physinfo(self->xc_handle, &pinfo) != 0 )
+            return pyxc_error_to_exception(self->xc_handle);
+
+        if ( arch_capabilities_arm_gic_v3(pinfo.arch_capabilities) )
+            config.arch.gic_version = XEN_DOMCTL_CONFIG_GIC_V3;
+        else if ( arch_capabilities_arm_gic_v2(pinfo.arch_capabilities) )
+            config.arch.gic_version = XEN_DOMCTL_CONFIG_GIC_V2;
+        else
+        {
+            errno = EINVAL;
+            PyErr_SetFromErrno(xc_error_obj);
+            return NULL;
+        }
+    }
 #else
 #error Architecture not supported
 #endif
-- 
2.53.0



--
Julian Vetter | Vates Hypervisor & Kernel Developer

XCP-ng & Xen Orchestra - Vates solutions

web: https://vates.tech