From 8673bedd76c2ae43acaeec1f78f3e4ec31088c77 Mon Sep 17 00:00:00 2001
From: Andrew Cooper <andrew.cooper3@citrix.com>
Date: Mon, 12 Oct 2026 15:42:03 +0200
Subject: [PATCH] ARM/sysctl: Expose the supported guest GIC modes in physinfo

In preparation to simplify the domain creation logic surrounding GIC
version.

On a GICv3 host, also report support for GICv2-compatible guests when
the hardware's vGICv2 compatibility mode is enabled, rather than just
the native GIC version.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Julian Vetter <julian.vetter@vates.tech>
Reviewed-by: Michal Orzel <michal.orzel@amd.com>
---
 xen/arch/arm/include/asm/vgic.h |  6 ++++++
 xen/arch/arm/sysctl.c           | 29 +++++++++++++++++++++++++++++
 xen/arch/arm/vgic-v2.c          |  5 +++++
 xen/arch/arm/vgic/vgic-v2.c     |  5 +++++
 xen/include/public/sysctl.h     |  2 ++
 5 files changed, 47 insertions(+)

diff --git a/xen/arch/arm/include/asm/vgic.h b/xen/arch/arm/include/asm/vgic.h
index 6f9ab1c98c..26c53aaf3c 100644
--- a/xen/arch/arm/include/asm/vgic.h
+++ b/xen/arch/arm/include/asm/vgic.h
@@ -433,6 +433,12 @@ unsigned int vgic_max_vcpus(unsigned int domctl_vgic_version);
 void vgic_v2_setup_hw(paddr_t dbase, paddr_t cbase, paddr_t csize,
                       paddr_t vbase, uint32_t aliased_offset);
 
+#ifdef CONFIG_VGICV2
+bool vgic_v2_hw_enabled(void);
+#else
+static inline bool vgic_v2_hw_enabled(void) { return false; }
+#endif
+
 #ifdef CONFIG_GICV3
 struct rdist_region;
 void vgic_v3_setup_hw(paddr_t dbase,
diff --git a/xen/arch/arm/sysctl.c b/xen/arch/arm/sysctl.c
index 32cab4feff..8de4027b9c 100644
--- a/xen/arch/arm/sysctl.c
+++ b/xen/arch/arm/sysctl.c
@@ -12,7 +12,11 @@
 #include <xen/dt-overlay.h>
 #include <xen/errno.h>
 #include <xen/hypercall.h>
+
 #include <asm/arm64/sve.h>
+#include <asm/gic.h>
+#include <asm/vgic.h>
+
 #include <public/sysctl.h>
 
 void arch_do_physinfo(struct xen_sysctl_physinfo *pi)
@@ -21,6 +25,31 @@ void arch_do_physinfo(struct xen_sysctl_physinfo *pi)
 
     pi->arch_capabilities |= MASK_INSR(sve_encode_vl(get_sys_vl_len()),
                                        XEN_SYSCTL_PHYSCAP_ARM_SVE_MASK);
+
+    switch ( gic_hw_version() )
+    {
+    case GIC_V2:
+        pi->arch_capabilities |= XEN_SYSCTL_PHYSCAP_ARM_GIC_V2;
+        break;
+
+    case GIC_V3:
+        pi->arch_capabilities |= XEN_SYSCTL_PHYSCAP_ARM_GIC_V3;
+
+        /* GICv3 may additionally support GICv2-compatible guests. */
+        if ( vgic_v2_hw_enabled() )
+            pi->arch_capabilities |= XEN_SYSCTL_PHYSCAP_ARM_GIC_V2;
+        break;
+
+    default:
+        /*
+         * Running a control domain without having the GIC sorted yet?
+         * Something's broken, but there's nothing we can do about it here.
+         */
+        printk_once(XENLOG_ERR "Unrecognised GIC version %d\n",
+                    gic_hw_version());
+        ASSERT_UNREACHABLE();
+        break;
+    }
 }
 
 long arch_do_sysctl(struct xen_sysctl *sysctl,
diff --git a/xen/arch/arm/vgic-v2.c b/xen/arch/arm/vgic-v2.c
index 6328ce6f7e..62666a84db 100644
--- a/xen/arch/arm/vgic-v2.c
+++ b/xen/arch/arm/vgic-v2.c
@@ -49,6 +49,11 @@ void __init vgic_v2_setup_hw(paddr_t dbase, paddr_t cbase, paddr_t csize,
     vgic_v2_hw.aliased_offset = aliased_offset;
 }
 
+bool vgic_v2_hw_enabled(void)
+{
+    return vgic_v2_hw.enabled;
+}
+
 #define NR_TARGETS_PER_ITARGETSR    4U
 #define NR_BITS_PER_TARGET  (32U / NR_TARGETS_PER_ITARGETSR)
 
diff --git a/xen/arch/arm/vgic/vgic-v2.c b/xen/arch/arm/vgic/vgic-v2.c
index 06fa365453..f6a58ed89e 100644
--- a/xen/arch/arm/vgic/vgic-v2.c
+++ b/xen/arch/arm/vgic/vgic-v2.c
@@ -47,6 +47,11 @@ void __init vgic_v2_setup_hw(paddr_t dbase, paddr_t cbase, paddr_t csize,
     printk("Using the new VGIC implementation.\n");
 }
 
+bool vgic_v2_hw_enabled(void)
+{
+    return gic_v2_hw_data.enabled;
+}
+
 /*
  * transfer the content of the LRs back into the corresponding ap_list:
  * - active bit is transferred as is
diff --git a/xen/include/public/sysctl.h b/xen/include/public/sysctl.h
index 63d0ee062b..a1216d7287 100644
--- a/xen/include/public/sysctl.h
+++ b/xen/include/public/sysctl.h
@@ -106,6 +106,8 @@ struct xen_sysctl_tbuf_op {
 
 #if defined(__arm__) || defined(__aarch64__)
 #define XEN_SYSCTL_PHYSCAP_ARM_SVE_MASK  (0x1FU)
+#define XEN_SYSCTL_PHYSCAP_ARM_GIC_V2    (1U << 5)
+#define XEN_SYSCTL_PHYSCAP_ARM_GIC_V3    (1U << 6)
 #endif
 
 struct xen_sysctl_physinfo {