git: 7b6be0014a4e - main - Hyper-V: Detect Extended Destination ID support

The branch main has been updated by cperciva:

URL: https://cgit.FreeBSD.org/src/commit/?id=7b6be0014a4eb81943491122bae70914b7fd82b6

commit 7b6be0014a4eb81943491122bae70914b7fd82b6
Author:     Colin Percival <cperciva@FreeBSD.org>
AuthorDate: 2026-02-22 04:09:01 +0000
Commit:     Colin Percival <cperciva@FreeBSD.org>
CommitDate: 2026-03-28 05:54:59 +0000

    Hyper-V: Detect Extended Destination ID support
    
    Hyper-V advertises support for the Extended Destination ID standard via
    bit 2 of the value returned in the EAX register when the hypervisor
    stack properties are queried via CPUID.
    
    This is based on a commit to the Linux kernel, as there does not seem
    to be any other documentation of this feature.
    
    Reviewed by:    Souradeep Chakrabarti
    MFC after:      3 weeks
    Sponsored by:   Amazon
    Differential Revision:  https://reviews.freebsd.org/D55432
---
 sys/dev/hyperv/vmbus/x86/hyperv_reg.h | 6 ++++++
 sys/x86/x86/local_apic.c              | 9 +++++++++
 2 files changed, 15 insertions(+)

diff --git a/sys/dev/hyperv/vmbus/x86/hyperv_reg.h b/sys/dev/hyperv/vmbus/x86/hyperv_reg.h
index 0597a1fea953..e7560d00f25e 100644
--- a/sys/dev/hyperv/vmbus/x86/hyperv_reg.h
+++ b/sys/dev/hyperv/vmbus/x86/hyperv_reg.h
@@ -45,4 +45,10 @@
 #define CPUID_LEAF_HV_IDENTITY		0x40000002
 #define CPUID_LEAF_HV_FEATURES		0x40000003
 #define CPUID_LEAF_HV_RECOMMENDS	0x40000004
+
+#define CPUID_LEAF_HV_STACK_INTERFACE	0x40000081
+#define HYPERV_STACK_INTERFACE_EAX_SIG	0x31235356	/* "VS#1" */
+#define CPUID_LEAF_HV_STACK_PROPERTIES	0x40000082
+#define HYPERV_PROPERTIES_EXT_DEST_ID	0x00000004
+
 #endif	/* !_HYPERV_REG_H_ */
diff --git a/sys/x86/x86/local_apic.c b/sys/x86/x86/local_apic.c
index 20f095a13574..cd5e4d474080 100644
--- a/sys/x86/x86/local_apic.c
+++ b/sys/x86/x86/local_apic.c
@@ -75,6 +75,7 @@
 #include <x86/kvm.h>
 #include <contrib/xen/arch-x86/cpuid.h>
 #include <x86/bhyve.h>
+#include <dev/hyperv/vmbus/x86/hyperv_reg.h>
 
 #ifdef DDB
 #include <sys/interrupt.h>
@@ -2107,6 +2108,14 @@ detect_extended_dest_id(void)
 		if (regs[0] & XEN_HVM_CPUID_EXT_DEST_ID)
 			apic_ext_dest_id = 1;
 		break;
+	case VM_GUEST_HV:
+		cpuid_count(CPUID_LEAF_HV_STACK_INTERFACE, 0, regs);
+		if (regs[0] != HYPERV_STACK_INTERFACE_EAX_SIG)
+			break;
+		cpuid_count(CPUID_LEAF_HV_STACK_PROPERTIES, 0, regs);
+		if (regs[0] & HYPERV_PROPERTIES_EXT_DEST_ID)
+			apic_ext_dest_id = 1;
+		break;
 	case VM_GUEST_KVM:
 		kvm_cpuid_get_features(regs);
 		if (regs[0] & KVM_FEATURE_MSI_EXT_DEST_ID)