git: 493676d3b271 - stable/15 - kvm: Support non-default CPUID leaf

The branch stable/15 has been updated by aokblast:

URL: https://cgit.FreeBSD.org/src/commit/?id=493676d3b2717c12ee09d84a5b73758f75a66278

commit 493676d3b2717c12ee09d84a5b73758f75a66278
Author:     ShengYi Hung <[email protected]>
AuthorDate: 2026-07-10 09:21:11 +0000
Commit:     ShengYi Hung <[email protected]>
CommitDate: 2026-07-25 13:13:24 +0000

    kvm: Support non-default CPUID leaf
    
    KVM does not always use 0x40000000 as its CPUID base. For example, QEMU
    adds a 0x100 offset when nested virtualization is detected and the host
    exposes Hyper-V enlightenment hints. To accommodate this behavior,
    switch the detection logic to use the CPUID leaf returned by do_cpuid(),
    making the implementation more flexible.
    
    See:
    https://github.com/qemu/qemu/blob/master/target/i386/kvm/kvm.c#L2300
    
    Reviewed by:    kib
    MFC after:      2 weeks
    Sponsored by:   The FreeBSD Foundation
    Differential Revision: https://reviews.freebsd.org/D58146
    
    (cherry picked from commit 86691d52a6d3796ad36ba474cf0a9493f6d99202)
---
 sys/x86/include/kvm.h | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/sys/x86/include/kvm.h b/sys/x86/include/kvm.h
index 83dd20fa8d23..5414075f89d6 100644
--- a/sys/x86/include/kvm.h
+++ b/sys/x86/include/kvm.h
@@ -45,7 +45,7 @@
 #include <machine/md_var.h>
 
 #define	KVM_CPUID_SIGNATURE			0x40000000
-#define	KVM_CPUID_FEATURES_LEAF			0x40000001
+#define	KVM_CPUID_FEATURES_LEAF(base)		((base) + 1)
 
 #define	KVM_FEATURE_CLOCKSOURCE			0x00000001
 #define	KVM_FEATURE_CLOCKSOURCE2		0x00000008
@@ -63,8 +63,7 @@ static inline bool
 kvm_cpuid_features_leaf_supported(void)
 {
 	return (vm_guest == VM_GUEST_KVM &&
-	    KVM_CPUID_FEATURES_LEAF > hv_base &&
-	    KVM_CPUID_FEATURES_LEAF <= hv_high);
+	    KVM_CPUID_FEATURES_LEAF(hv_base) <= hv_high);
 }
 
 static inline void
@@ -73,7 +72,7 @@ kvm_cpuid_get_features(u_int *regs)
 	if (!kvm_cpuid_features_leaf_supported())
 		regs[0] = regs[1] = regs[2] = regs[3] = 0;
 	else
-		do_cpuid(KVM_CPUID_FEATURES_LEAF, regs);
+		do_cpuid(KVM_CPUID_FEATURES_LEAF(hv_base), regs);
 }
 
 #endif /* !_X86_KVM_H_ */