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Date:      Thu, 16 Apr 2026 15:12:14 +0000
From:      Colin Percival <cperciva@FreeBSD.org>
To:        src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-branches@FreeBSD.org
Cc:        David Woodhouse <dwmw@amazon.co.uk>
Subject:   git: 020a2480f553 - stable/14 - bhyve: Add CPUID_BHYVE_FEATURES leaf
Message-ID:  <69e0fc4e.1c6f7.1a36b66e@gitrepo.freebsd.org>
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The branch stable/14 has been updated by cperciva:

URL: https://cgit.FreeBSD.org/src/commit/?id=020a2480f55303f757e9683d05213ae3266e7831

commit 020a2480f55303f757e9683d05213ae3266e7831
Author:     David Woodhouse <dwmw@amazon.co.uk>
AuthorDate: 2025-08-11 10:44:05 +0000
Commit:     Colin Percival <cperciva@FreeBSD.org>
CommitDate: 2026-04-16 15:11:41 +0000

    bhyve: Add CPUID_BHYVE_FEATURES leaf
    
    This allows the hypervisor to advertise features to the guest. The first
    such feature is CPUID_BHYVE_EXT_DEST_ID which advertises that 15 bits
    of target APIC ID are available in MSI (and I/O APIC) interrupts, as
    documented in http://david.woodhou.se/ExtDestId.pdf
    
    This defines the guest ABI. The actual implementation will come in a
    subsequent commit.
    
    Reviewed by: kib
    Pull Request: https://github.com/freebsd/freebsd-src/pull/1797
    Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
    (cherry picked from commit 313a68ea20b48629f655cf38987f4a6ff822f1ab)
---
 sys/amd64/vmm/x86.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/sys/amd64/vmm/x86.c b/sys/amd64/vmm/x86.c
index 744e2bfd57db..eea334562784 100644
--- a/sys/amd64/vmm/x86.c
+++ b/sys/amd64/vmm/x86.c
@@ -49,7 +49,12 @@ SYSCTL_DECL(_hw_vmm);
 static SYSCTL_NODE(_hw_vmm, OID_AUTO, topology, CTLFLAG_RD | CTLFLAG_MPSAFE, 0,
     NULL);
 
-#define	CPUID_VM_HIGH		0x40000000
+#define CPUID_VM_SIGNATURE	0x40000000
+#define CPUID_BHYVE_FEATURES	0x40000001
+#define	CPUID_VM_HIGH		CPUID_BHYVE_FEATURES
+
+/* Features advertised in CPUID_BHYVE_FEATURES %eax */
+#define CPUID_BHYVE_FEAT_EXT_DEST_ID	(1UL << 0) /* MSI Extended Dest ID */
 
 static const char bhyve_id[12] = "bhyve bhyve ";
 
@@ -102,7 +107,7 @@ x86_emulate_cpuid(struct vcpu *vcpu, uint64_t *rax, uint64_t *rbx,
 	if (cpu_exthigh != 0 && func >= 0x80000000) {
 		if (func > cpu_exthigh)
 			func = cpu_exthigh;
-	} else if (func >= 0x40000000) {
+	} else if (func >= CPUID_VM_SIGNATURE) {
 		if (func > CPUID_VM_HIGH)
 			func = CPUID_VM_HIGH;
 	} else if (func > cpu_high) {
@@ -603,13 +608,20 @@ x86_emulate_cpuid(struct vcpu *vcpu, uint64_t *rax, uint64_t *rbx,
 			regs[3] = 0;
 			break;
 
-		case 0x40000000:
+		case CPUID_VM_SIGNATURE:
 			regs[0] = CPUID_VM_HIGH;
 			bcopy(bhyve_id, &regs[1], 4);
 			bcopy(bhyve_id + 4, &regs[2], 4);
 			bcopy(bhyve_id + 8, &regs[3], 4);
 			break;
 
+		case CPUID_BHYVE_FEATURES:
+			regs[0] = 0; /* No features to advertise yet */
+			regs[1] = 0;
+			regs[2] = 0;
+			regs[3] = 0;
+			break;
+
 		default:
 default_leaf:
 			/*
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