on several similarly-config'd machines running

	distro
		Name: Fedora Linux 42 (Adams)
		Version: 42
		Codename:

with

	rpm -qa | grep kernel-6
		kernel-6.15.3-200.fc42.x86_64
		kernel-6.15.4-200.fc42.x86_64
		kernel-6.15.5-200.fc42.x86_64

on AMD cpu,

	cat /proc/cpuinfo  |  grep -E "model name|flags" | head -n2
		model name      : AMD Ryzen 5 5600G with Radeon Graphics
		flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt pdpe1gb rdtscp lm constant_tsc rep_good nopl xtopology nonstop_tsc cpuid extd_apicid aperfmperf rapl pni pclmulqdq monitor ssse3 fma cx16 sse4_1 sse4_2 x2apic movbe popcnt aes xsave avx f16c rdrand lahf_lm cmp_legacy svm extapic cr8_legacy abm sse4a misalignsse 3dnowprefetch osvw ibs skinit wdt tce topoext perfctr_core perfctr_nb bpext perfctr_llc mwaitx cpb cat_l3 cdp_l3 hw_pstate ssbd mba ibrs ibpb stibp vmmcall fsgsbase bmi1 avx2 smep bmi2 erms invpcid cqm rdt_a rdseed adx smap clflushopt clwb sha_ni xsaveopt xsavec xgetbv1 xsaves cqm_llc cqm_occup_llc cqm_mbm_total cqm_mbm_local user_shstk clzero irperf xsaveerptr rdpru wbnoinvd cppc arat npt lbrv svm_lock nrip_save tsc_scale vmcb_clean flushbyasid decodeassists pausefilter pfthreshold avic v_vmsave_vmload vgif v_spec_ctrl umip pku ospke vaes vpclmulqdq rdpid overflow_recov succor smca fsrm debug_swap

when booted to either of

	uname -rm
		6.15.3-200.fc42.x86_64 x86_64

	uname -rm
		6.15.4-200.fc42.x86_64 x86_64

KVM guests launche without issue; e.g.

	virsh list
		 Id   Name   State
		----------------------
		 1    f01    running

	virsh dominfo f01
		Id:             1
		Name:           f01
		UUID:           f...
		OS Type:        hvm
		State:          running
		CPU(s):         4
		CPU time:       44.1s
		Max memory:     8388608 KiB
		Used memory:    8388608 KiB
		Persistent:     yes
		Autostart:      enable
		Managed save:   no
		Security model: none
		Security DOI:   0

on switch to

	uname -rm
		6.15.5-200.fc42.x86_64 x86_64

, with no other changes, kvm guest fails to launch

	Jul 13 16:17:26 mach virtqemud[1831]: internal error: Failed to autostart VM 'f01': operation failed: guest CPU doesn't match specification: missing features: sbpb,ibpb-brtype

reboot, switch to

		6.15.3-200.fc42.x86_64 x86_64

or,

		6.15.4-200.fc42.x86_64 x86_64

all's good again.

here,

	rpm -q --whatprovides `which virtqemud`
		libvirt-daemon-driver-qemu-11.0.0-3.fc42.x86_64

	rpm -q --queryformat '%{installtime:date}\n' kernel-6.15.5-200.fc42.x86_64 libvirt-daemon-driver-qemu
		Sun 13 Jul 2025 12:19:01 PM EDT
		Tue 24 Jun 2025 07:33:57 PM EDT

digging re: sbpb & ibpb speculative exec barriers, i note @ 6.15 AMD-related changes

	Linux 6.15 Adds AMD Zen 5 SRSO Mitigation For KVM, Preps For Attack Vector Controls
	 https://www.phoronix.com/news/Linux-6.15-x86-bugs

checking

	cd /etc/libvirt/
	grep -E "cpu mode|sbpb|ibpb" `find . | grep xml`
		./qemu/autostart/f01.xml:  <cpu mode='custom' match='exact' check='full'>
		./qemu/autostart/f01.xml:    <feature policy='require' name='sbpb'/>
		./qemu/autostart/f01.xml:    <feature policy='require' name='ibpb-brtype'/>
		./qemu/f01.xml:  <cpu mode='custom' match='exact' check='full'>
		./qemu/f01.xml:    <feature policy='require' name='sbpb'/>
		./qemu/f01.xml:    <feature policy='require' name='ibpb-brtype'/>


Reproducible: Always