git: 313a68ea20b4 - main - bhyve: Add CPUID_BHYVE_FEATURES leaf

[Colin Percival]

The branch main has been updated by cperciva:

URL: 
https://cgit.FreeBSD.org/src/commit/?id=313a68ea20b48629f655cf38987f4a6ff822f1ab

commit 313a68ea20b48629f655cf38987f4a6ff822f1ab
Author:     David Woodhouse <d...@amazon.co.uk>
AuthorDate: 2025-08-11 10:44:05 +0000
Commit:     Colin Percival <cperc...@freebsd.org>
CommitDate: 2025-08-13 20:31:15 +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 <d...@amazon.co.uk>
---
 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 366f1da9f850..9c2fdac11a81 100644
--- a/sys/amd64/vmm/x86.c
+++ b/sys/amd64/vmm/x86.c
@@ -48,7 +48,12 @@ 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 ";
 
@@ -100,7 +105,7 @@ 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) {
@@ -601,13 +606,20 @@ 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:
                        /*