git: 2931aabc40ea - stable/15 - KVM: Detect Extended Destination ID support

The branch stable/15 has been updated by cperciva:

URL: https://cgit.FreeBSD.org/src/commit/?id=2931aabc40ea380781f882e0909fed75f8530b64

commit 2931aabc40ea380781f882e0909fed75f8530b64
Author:     Colin Percival <cperciva@FreeBSD.org>
AuthorDate: 2026-02-22 04:09:00 +0000
Commit:     Colin Percival <cperciva@FreeBSD.org>
CommitDate: 2026-04-16 15:03:59 +0000

    KVM: Detect Extended Destination ID support
    
    KVM advertises support for the Extended Destination ID standard via
    bit 15 of the value returned in the EAX register when KVM features
    are queried via CPUID.
    
    Tested on:      EC2 r8i.96xlarge
    MFC after:      3 weeks
    Sponsored by:   Amazon
    Differential Revision:  https://reviews.freebsd.org/D55427
    
    (cherry picked from commit 9ab5aa3d4c7879d5518afc7587a864ba880e7ee9)
---
 sys/x86/include/kvm.h    |  1 +
 sys/x86/x86/local_apic.c | 11 +++++++++++
 2 files changed, 12 insertions(+)

diff --git a/sys/x86/include/kvm.h b/sys/x86/include/kvm.h
index fef26bde226a..83dd20fa8d23 100644
--- a/sys/x86/include/kvm.h
+++ b/sys/x86/include/kvm.h
@@ -49,6 +49,7 @@
 
 #define	KVM_FEATURE_CLOCKSOURCE			0x00000001
 #define	KVM_FEATURE_CLOCKSOURCE2		0x00000008
+#define	KVM_FEATURE_MSI_EXT_DEST_ID		0x00008000
 #define	KVM_FEATURE_CLOCKSOURCE_STABLE_BIT	0x01000000
 
 /* Deprecated: for the CLOCKSOURCE feature. */
diff --git a/sys/x86/x86/local_apic.c b/sys/x86/x86/local_apic.c
index cb7b03b313c1..ea5b14d92262 100644
--- a/sys/x86/x86/local_apic.c
+++ b/sys/x86/x86/local_apic.c
@@ -72,6 +72,7 @@
 #include <machine/smp.h>
 #include <machine/specialreg.h>
 #include <x86/init.h>
+#include <x86/kvm.h>
 
 #ifdef DDB
 #include <sys/interrupt.h>
@@ -2076,6 +2077,16 @@ SYSCTL_INT(_machdep, OID_AUTO, apic_ext_dest_id, CTLFLAG_RDTUN, &apic_ext_dest_i
 static void
 detect_extended_dest_id(void)
 {
+	u_int regs[4];
+
+	/* Check if we support extended destination IDs. */
+	switch (vm_guest) {
+	case VM_GUEST_KVM:
+		kvm_cpuid_get_features(regs);
+		if (regs[0] & KVM_FEATURE_MSI_EXT_DEST_ID)
+			apic_ext_dest_id = 1;
+		break;
+	}
 }
 
 /*