This article is an updated version of the old QEMU article about CPU flags available for version 2.0.0 – QEMU full virtualization – CPU emulations (enable/disable CPU flags/instruction sets) of QEMU 2.0.0.
The latest version of QEMU is 6.2.0 and it offers way more CPU flags and features! You can use QEMU with a nearly native full virtualization. Here are some important tips for the guest CPU to consider when using QEMU directly (without any virtualization manager like virt-manager, libvirt and so on).
TIP 1)Choose your host CPU emulation
You can see what options are available for host emulation with:
root@srv ~ # qemu-system-x86_64 -cpu help Available CPUs: x86 486 (alias configured by machine type) x86 486-v1 x86 Broadwell (alias configured by machine type) x86 Broadwell-IBRS (alias of Broadwell-v3) x86 Broadwell-noTSX (alias of Broadwell-v2) x86 Broadwell-noTSX-IBRS (alias of Broadwell-v4) x86 Broadwell-v1 Intel Core Processor (Broadwell) x86 Broadwell-v2 Intel Core Processor (Broadwell, no TSX) x86 Broadwell-v3 Intel Core Processor (Broadwell, IBRS) x86 Broadwell-v4 Intel Core Processor (Broadwell, no TSX, IBRS) x86 Cascadelake-Server (alias configured by machine type) x86 Cascadelake-Server-noTSX (alias of Cascadelake-Server-v3) x86 Cascadelake-Server-v1 Intel Xeon Processor (Cascadelake) x86 Cascadelake-Server-v2 Intel Xeon Processor (Cascadelake) [ARCH_CAPABILITIES] x86 Cascadelake-Server-v3 Intel Xeon Processor (Cascadelake) [ARCH_CAPABILITIES, no TSX] x86 Cascadelake-Server-v4 Intel Xeon Processor (Cascadelake) [ARCH_CAPABILITIES, no TSX] x86 Conroe (alias configured by machine type) x86 Conroe-v1 Intel Celeron_4x0 (Conroe/Merom Class Core 2) x86 Cooperlake (alias configured by machine type) x86 Cooperlake-v1 Intel Xeon Processor (Cooperlake) x86 Denverton (alias configured by machine type) x86 Denverton-v1 Intel Atom Processor (Denverton) x86 Denverton-v2 Intel Atom Processor (Denverton) [no MPX, no MONITOR] x86 Dhyana (alias configured by machine type) x86 Dhyana-v1 Hygon Dhyana Processor x86 EPYC (alias configured by machine type) x86 EPYC-IBPB (alias of EPYC-v2) x86 EPYC-Milan (alias configured by machine type) x86 EPYC-Milan-v1 AMD EPYC-Milan Processor x86 EPYC-Rome (alias configured by machine type) x86 EPYC-Rome-v1 AMD EPYC-Rome Processor x86 EPYC-Rome-v2 AMD EPYC-Rome Processor x86 EPYC-v1 AMD EPYC Processor x86 EPYC-v2 AMD EPYC Processor (with IBPB) x86 EPYC-v3 AMD EPYC Processor x86 Haswell (alias configured by machine type) x86 Haswell-IBRS (alias of Haswell-v3) x86 Haswell-noTSX (alias of Haswell-v2) x86 Haswell-noTSX-IBRS (alias of Haswell-v4) x86 Haswell-v1 Intel Core Processor (Haswell) x86 Haswell-v2 Intel Core Processor (Haswell, no TSX) x86 Haswell-v3 Intel Core Processor (Haswell, IBRS) x86 Haswell-v4 Intel Core Processor (Haswell, no TSX, IBRS) x86 Icelake-Client (alias configured by machine type) x86 Icelake-Client-noTSX (alias of Icelake-Client-v2) x86 Icelake-Client-v1 Intel Core Processor (Icelake) [deprecated] x86 Icelake-Client-v2 Intel Core Processor (Icelake) [no TSX, deprecated] x86 Icelake-Server (alias configured by machine type) x86 Icelake-Server-noTSX (alias of Icelake-Server-v2) x86 Icelake-Server-v1 Intel Xeon Processor (Icelake) x86 Icelake-Server-v2 Intel Xeon Processor (Icelake) [no TSX] x86 Icelake-Server-v3 Intel Xeon Processor (Icelake) x86 Icelake-Server-v4 Intel Xeon Processor (Icelake) x86 IvyBridge (alias configured by machine type) x86 IvyBridge-IBRS (alias of IvyBridge-v2) x86 IvyBridge-v1 Intel Xeon E3-12xx v2 (Ivy Bridge) x86 IvyBridge-v2 Intel Xeon E3-12xx v2 (Ivy Bridge, IBRS) x86 KnightsMill (alias configured by machine type) x86 KnightsMill-v1 Intel Xeon Phi Processor (Knights Mill) x86 Nehalem (alias configured by machine type) x86 Nehalem-IBRS (alias of Nehalem-v2) x86 Nehalem-v1 Intel Core i7 9xx (Nehalem Class Core i7) x86 Nehalem-v2 Intel Core i7 9xx (Nehalem Core i7, IBRS update) x86 Opteron_G1 (alias configured by machine type) x86 Opteron_G1-v1 AMD Opteron 240 (Gen 1 Class Opteron) x86 Opteron_G2 (alias configured by machine type) x86 Opteron_G2-v1 AMD Opteron 22xx (Gen 2 Class Opteron) x86 Opteron_G3 (alias configured by machine type) x86 Opteron_G3-v1 AMD Opteron 23xx (Gen 3 Class Opteron) x86 Opteron_G4 (alias configured by machine type) x86 Opteron_G4-v1 AMD Opteron 62xx class CPU x86 Opteron_G5 (alias configured by machine type) x86 Opteron_G5-v1 AMD Opteron 63xx class CPU x86 Penryn (alias configured by machine type) x86 Penryn-v1 Intel Core 2 Duo P9xxx (Penryn Class Core 2) x86 SandyBridge (alias configured by machine type) x86 SandyBridge-IBRS (alias of SandyBridge-v2) x86 SandyBridge-v1 Intel Xeon E312xx (Sandy Bridge) x86 SandyBridge-v2 Intel Xeon E312xx (Sandy Bridge, IBRS update) x86 Skylake-Client (alias configured by machine type) x86 Skylake-Client-IBRS (alias of Skylake-Client-v2) x86 Skylake-Client-noTSX-IBRS (alias of Skylake-Client-v3) x86 Skylake-Client-v1 Intel Core Processor (Skylake) x86 Skylake-Client-v2 Intel Core Processor (Skylake, IBRS) x86 Skylake-Client-v3 Intel Core Processor (Skylake, IBRS, no TSX) x86 Skylake-Server (alias configured by machine type) x86 Skylake-Server-IBRS (alias of Skylake-Server-v2) x86 Skylake-Server-noTSX-IBRS (alias of Skylake-Server-v3) x86 Skylake-Server-v1 Intel Xeon Processor (Skylake) x86 Skylake-Server-v2 Intel Xeon Processor (Skylake, IBRS) x86 Skylake-Server-v3 Intel Xeon Processor (Skylake, IBRS, no TSX) x86 Skylake-Server-v4 Intel Xeon Processor (Skylake, IBRS, no TSX) x86 Snowridge (alias configured by machine type) x86 Snowridge-v1 Intel Atom Processor (SnowRidge) x86 Snowridge-v2 Intel Atom Processor (Snowridge, no MPX) x86 Westmere (alias configured by machine type) x86 Westmere-IBRS (alias of Westmere-v2) x86 Westmere-v1 Westmere E56xx/L56xx/X56xx (Nehalem-C) x86 Westmere-v2 Westmere E56xx/L56xx/X56xx (IBRS update) x86 athlon (alias configured by machine type) x86 athlon-v1 QEMU Virtual CPU version 2.5+ x86 core2duo (alias configured by machine type) x86 core2duo-v1 Intel(R) Core(TM)2 Duo CPU T7700 @ 2.40GHz x86 coreduo (alias configured by machine type) x86 coreduo-v1 Genuine Intel(R) CPU T2600 @ 2.16GHz x86 kvm32 (alias configured by machine type) x86 kvm32-v1 Common 32-bit KVM processor x86 kvm64 (alias configured by machine type) x86 kvm64-v1 Common KVM processor x86 n270 (alias configured by machine type) x86 n270-v1 Intel(R) Atom(TM) CPU N270 @ 1.60GHz x86 pentium (alias configured by machine type) x86 pentium-v1 x86 pentium2 (alias configured by machine type) x86 pentium2-v1 x86 pentium3 (alias configured by machine type) x86 pentium3-v1 x86 phenom (alias configured by machine type) x86 phenom-v1 AMD Phenom(tm) 9550 Quad-Core Processor x86 qemu32 (alias configured by machine type) x86 qemu32-v1 QEMU Virtual CPU version 2.5+ x86 qemu64 (alias configured by machine type) x86 qemu64-v1 QEMU Virtual CPU version 2.5+ x86 base base CPU model type with no features enabled x86 host KVM processor with all supported host features x86 max Enables all features supported by the accelerator in the current host Recognized CPUID flags: 3dnow 3dnowext 3dnowprefetch abm ace2 ace2-en acpi adx aes amd-no-ssb amd-ssbd amd-stibp apic arat arch-capabilities avic avx avx2 avx512-4fmaps avx512-4vnniw avx512-bf16 avx512-fp16 avx512-vp2intersect avx512-vpopcntdq avx512bitalg avx512bw avx512cd avx512dq avx512er avx512f avx512ifma avx512pf avx512vbmi avx512vbmi2 avx512vl avx512vnni bmi1 bmi2 bus-lock-detect cid cldemote clflush clflushopt clwb clzero cmov cmp-legacy core-capability cr8legacy cx16 cx8 dca de decodeassists ds ds-cpl dtes64 erms est extapic f16c flushbyasid fma fma4 fpu fsgsbase fsrm full-width-write fxsr fxsr-opt gfni hle ht hypervisor ia64 ibpb ibrs ibrs-all ibs intel-pt intel-pt-lip invpcid invtsc kvm-asyncpf kvm-asyncpf-int kvm-hint-dedicated kvm-mmu kvm-msi-ext-dest-id kvm-nopiodelay kvm-poll-control kvm-pv-eoi kvm-pv-ipi kvm-pv-sched-yield kvm-pv-tlb-flush kvm-pv-unhalt kvm-steal-time kvmclock kvmclock kvmclock-stable-bit la57 lahf-lm lbrv lm lwp mca mce md-clear mds-no misalignsse mmx mmxext monitor movbe movdir64b movdiri mpx msr mtrr nodeid-msr npt nrip-save nx osvw pae pat pause-filter pbe pcid pclmulqdq pcommit pdcm pdpe1gb perfctr-core perfctr-nb pfthreshold pge phe phe-en pks pku pmm pmm-en pn pni popcnt pschange-mc-no pse pse36 rdctl-no rdpid rdrand rdseed rdtscp rsba rtm sep serialize sha-ni skinit skip-l1dfl-vmentry smap smep smx spec-ctrl split-lock-detect ss ssb-no ssbd sse sse2 sse4.1 sse4.2 sse4a ssse3 stibp svm svm-lock svme-addr-chk syscall taa-no tbm tce tm tm2 topoext tsc tsc-adjust tsc-deadline tsc-scale tsx-ctrl tsx-ldtrk umip v-vmsave-vmload vaes vgif virt-ssbd vmcb-clean vme vmx vmx-activity-hlt vmx-activity-shutdown vmx-activity-wait-sipi vmx-apicv-register vmx-apicv-vid vmx-apicv-x2apic vmx-apicv-xapic vmx-cr3-load-noexit vmx-cr3-store-noexit vmx-cr8-load-exit vmx-cr8-store-exit vmx-desc-exit vmx-encls-exit vmx-entry-ia32e-mode vmx-entry-load-bndcfgs vmx-entry-load-efer vmx-entry-load-pat vmx-entry-load-perf-global-ctrl vmx-entry-load-pkrs vmx-entry-load-rtit-ctl vmx-entry-noload-debugctl vmx-ept vmx-ept-1gb vmx-ept-2mb vmx-ept-advanced-exitinfo vmx-ept-execonly vmx-eptad vmx-eptp-switching vmx-exit-ack-intr vmx-exit-clear-bndcfgs vmx-exit-clear-rtit-ctl vmx-exit-load-efer vmx-exit-load-pat vmx-exit-load-perf-global-ctrl vmx-exit-load-pkrs vmx-exit-nosave-debugctl vmx-exit-save-efer vmx-exit-save-pat vmx-exit-save-preemption-timer vmx-flexpriority vmx-hlt-exit vmx-ins-outs vmx-intr-exit vmx-invept vmx-invept-all-context vmx-invept-single-context vmx-invept-single-context vmx-invept-single-context-noglobals vmx-invlpg-exit vmx-invpcid-exit vmx-invvpid vmx-invvpid-all-context vmx-invvpid-single-addr vmx-io-bitmap vmx-io-exit vmx-monitor-exit vmx-movdr-exit vmx-msr-bitmap vmx-mtf vmx-mwait-exit vmx-nmi-exit vmx-page-walk-4 vmx-page-walk-5 vmx-pause-exit vmx-ple vmx-pml vmx-posted-intr vmx-preemption-timer vmx-rdpmc-exit vmx-rdrand-exit vmx-rdseed-exit vmx-rdtsc-exit vmx-rdtscp-exit vmx-secondary-ctls vmx-shadow-vmcs vmx-store-lma vmx-true-ctls vmx-tsc-offset vmx-unrestricted-guest vmx-vintr-pending vmx-vmfunc vmx-vmwrite-vmexit-fields vmx-vnmi vmx-vnmi-pending vmx-vpid vmx-wbinvd-exit vmx-xsaves vmx-zero-len-inject vpclmulqdq waitpkg wbnoinvd wdt x2apic xcrypt xcrypt-en xgetbv1 xop xsave xsavec xsaveerptr xsaveopt xsaves xstore xstore-en xtpr
The number of supported flags grew enormously compared to the old versions of QEMU and in fact, they include almost all available CPU flags. The supported CPUs are also several times more than before! The above list of supported CPUs means the virtual guest machine could use one of them and the guest operating system will have all the flags the CPU supports. In fact, the guest virtual system will report to the OS it has the selected CPU from the list above.
If the user does not want to export the real host CPU, the qemu64 and additional flags could be manually added to the qemu-system-x86_64 command-line:
qemu-system-x86_64 -enable-kvm -cpu qemu64,+ssse3,+sse4.1,+sse4.2,+x2apic \ -smp 2,maxcpus=8 -daemonize -vnc 127.0.0.1:1 \ -drive file=/srv/qemu/test/test.qcow2,index=0,cache=none,aio=threads,if=virtio \ -cdrom /srv/qemu/test/install-amd64-minimal-20201227T214503Z.iso -boot d \ -m 8192 -net nic,model=virtio,macaddr=00:00:00:00:00:01 \ -net tap,ifname=tap0,script=no,downscript=no \ -monitor telnet:127.0.0.1:5801,server,nowait \ -writeconfig /srv/qemu/test/test.qcow2.conf
The guest server (the virtual machine) will have the following CPU and instructions set:
livecd ~ # cat /proc/cpuinfo processor : 0 vendor_id : AuthenticAMD cpu family : 6 model : 6 model name : QEMU Virtual CPU version 2.5+ stepping : 3 microcode : 0x1000065 cpu MHz : 3393.624 cache size : 512 KB physical id : 0 siblings : 1 core id : 0 cpu cores : 1 apicid : 0 initial apicid : 0 fpu : yes fpu_exception : yes cpuid level : 13 wp : yes flags : fpu de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 syscall nx lm nopl cpuid tsc_known_freq pni ssse3 cx16 sse4_1 sse4_2 x2apic hypervisor lahf_lm 3dnowprefetch vmmcall bugs : fxsave_leak sysret_ss_attrs null_seg spectre_v1 spectre_v2 spec_store_bypass bogomips : 6787.24 TLB size : 1024 4K pages clflush size : 64 cache_alignment : 64 address sizes : 40 bits physical, 48 bits virtual power management: processor : 1 vendor_id : AuthenticAMD cpu family : 6 model : 6 model name : QEMU Virtual CPU version 2.5+ stepping : 3 microcode : 0x1000065 cpu MHz : 3393.624 cache size : 512 KB physical id : 1 siblings : 1 core id : 0 cpu cores : 1 apicid : 1 initial apicid : 1 fpu : yes fpu_exception : yes cpuid level : 13 wp : yes flags : fpu de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 syscall nx lm nopl cpuid tsc_known_freq pni ssse3 cx16 sse4_1 sse4_2 x2apic hypervisor lahf_lm 3dnowprefetch vmmcall bugs : fxsave_leak sysret_ss_attrs null_seg spectre_v1 spectre_v2 spec_store_bypass bogomips : 6787.24 TLB size : 1024 4K pages clflush size : 64 cache_alignment : 64 address sizes : 40 bits physical, 48 bits virtual power management:
Compare it with the original host CPU:
livecd ~ # cat /proc/cpuinfo processor : 0 vendor_id : AuthenticAMD cpu family : 23 model : 1 model name : AMD Ryzen Threadripper 1950X 16-Core Processor stepping : 1 microcode : 0x8001137 cpu MHz : 1982.087 cache size : 512 KB physical id : 0 siblings : 32 core id : 0 cpu cores : 16 apicid : 0 initial apicid : 0 fpu : yes fpu_exception : yes cpuid level : 13 wp : yes 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 nonstop_tsc cpuid extd_apicid amd_dcm aperfmperf pni pclmulqdq monitor ssse3 fma cx16 sse4_1 sse4_2 movbe popcnt aes xsave avx f16c rdrand lahf_lm cmp_legacy svm extapic cr8_legacy abm sse4a misalignsse 3dnowprefetch osvw skinit wdt tce topoext perfctr_core perfctr_nb bpext perfctr_llc mwaitx cpb hw_pstate sme ssbd sev ibpb vmmcall fsgsbase bmi1 avx2 smep bmi2 rdseed adx smap clflushopt sha_ni xsaveopt xsavec xgetbv1 xsaves clzero irperf xsaveerptr arat npt lbrv svm_lock nrip_save tsc_scale vmcb_clean flushbyasid decodeassists pausefilter pfthreshold avic v_vmsave_vmload vgif overflow_recov succor smca bugs : sysret_ss_attrs null_seg spectre_v1 spectre_v2 spec_store_bypass bogomips : 6786.60 TLB size : 2560 4K pages clflush size : 64 cache_alignment : 64 address sizes : 43 bits physical, 48 bits virtual power management: ts ttp tm hwpstate eff_freq_ro [13] [14]
The QEMU preseved the CPU type – AuthenticAMD, bogomips and the original base clock of the CPU, which is 3.4Ghz.
To enable a specific processor family, the host CPU should support all the instruction sets of the requested CPU. So AuthenticAMD cannot support Broadwell-v3:
root@srv ~ # qemu-system-x86_64 -enable-kvm -cpu Broadwell-v3 -smp 2,maxcpus=8 -daemonize -vnc 192.168.0.15:1 -drive file=/srv/qemu/test/test.qcow2,index=0,cache=none,aio=threads,if=virtio -cdrom /srv/qemu/test/install-amd64-minimal-20201227T214503Z.iso -boot d -m 8192 -net nic,model=virtio,macaddr=e6:2b:b3:40:81:0c -net tap,ifname=tap0,script=no,downscript=no -monitor telnet:127.0.0.1:5801,server,nowait -writeconfig /srv/qemu/test/test.qcow2.conf qemu-system-x86_64: -writeconfig /srv/qemu/test/test.qcow2.conf: warning: -writeconfig is deprecated and will go away without a replacement qemu-system-x86_64: warning: host doesn't support requested feature: CPUID.01H:ECX.pcid [bit 17] qemu-system-x86_64: warning: host doesn't support requested feature: CPUID.07H:EBX.hle [bit 4] qemu-system-x86_64: warning: host doesn't support requested feature: CPUID.07H:EBX.erms [bit 9] qemu-system-x86_64: warning: host doesn't support requested feature: CPUID.07H:EBX.invpcid [bit 10] qemu-system-x86_64: warning: host doesn't support requested feature: CPUID.07H:EBX.rtm [bit 11] qemu-system-x86_64: warning: host doesn't support requested feature: CPUID.07H:EDX.spec-ctrl [bit 26] qemu-system-x86_64: warning: host doesn't support requested feature: CPUID.01H:ECX.pcid [bit 17] qemu-system-x86_64: warning: host doesn't support requested feature: CPUID.07H:EBX.hle [bit 4] qemu-system-x86_64: warning: host doesn't support requested feature: CPUID.07H:EBX.erms [bit 9] qemu-system-x86_64: warning: host doesn't support requested feature: CPUID.07H:EBX.invpcid [bit 10] qemu-system-x86_64: warning: host doesn't support requested feature: CPUID.07H:EBX.rtm [bit 11] qemu-system-x86_64: warning: host doesn't support requested feature: CPUID.07H:EDX.spec-ctrl [bit 26]
There are multiple warnings that the host server does not support a feature it should, to emulate the selected processor.
Still, the virtual guest system boots successfully:
livecd ~ # cat /proc/cpuinfo processor : 0 vendor_id : AuthenticAMD cpu family : 6 model : 61 model name : Intel Core Processor (Broadwell, IBRS) stepping : 2 microcode : 0x1000065 cpu MHz : 3393.624 cache size : 512 KB physical id : 0 siblings : 1 core id : 0 cpu cores : 1 apicid : 0 initial apicid : 0 fpu : yes fpu_exception : yes cpuid level : 13 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 syscall nx rdtscp lm nopl cpuid tsc_known_freq pni pclmulqdq ssse3 fma cx16 sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand hypervisor lahf_lm abm 3dnowprefetch vmmcall fsgsbase bmi1 avx2 smep bmi2 rdseed adx smap xsaveopt arat bugs : fxsave_leak sysret_ss_attrs null_seg spectre_v1 spectre_v2 spec_store_bypass bogomips : 6787.24 TLB size : 1024 4K pages clflush size : 64 cache_alignment : 64 address sizes : 40 bits physical, 48 bits virtual power management: processor : 1 vendor_id : AuthenticAMD cpu family : 6 model : 61 model name : Intel Core Processor (Broadwell, IBRS) stepping : 2 microcode : 0x1000065 cpu MHz : 3393.624 cache size : 512 KB physical id : 1 siblings : 1 core id : 0 cpu cores : 1 apicid : 1 initial apicid : 1 fpu : yes fpu_exception : yes cpuid level : 13 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 syscall nx rdtscp lm nopl cpuid tsc_known_freq pni pclmulqdq ssse3 fma cx16 sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand hypervisor lahf_lm abm 3dnowprefetch vmmcall fsgsbase bmi1 avx2 smep bmi2 rdseed adx smap xsaveopt arat bugs : fxsave_leak sysret_ss_attrs null_seg spectre_v1 spectre_v2 spec_store_bypass bogomips : 6787.24 TLB size : 1024 4K pages clflush size : 64 cache_alignment : 64 address sizes : 40 bits physical, 48 bits virtual power management:
Note, the vendor_id is AuthenticAMD and the model name is Intel Core Processor (Broadwell, IBRS). Such things may lead to bugs under the guest OS!!!
To change the vendor_id, the KVM (–enable-kvm) should be turned off, so the hardware support in the CPU would be disabled for the guest system and the virtualization will be slower:
livecd ~ # cat /proc/cpuinfo processor : 0 vendor_id : GenuineIntel cpu family : 6 model : 61 model name : Intel Core Processor (Broadwell, IBRS) stepping : 2 microcode : 0x1 cpu MHz : 3393.641 cache size : 16384 KB physical id : 0 siblings : 1 core id : 0 cpu cores : 1 apicid : 0 initial apicid : 0 fpu : yes fpu_exception : yes cpuid level : 13 wp : yes flags : fpu de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 syscall nx rdtscp lm constant_tsc rep_good nopl xtopology cpuid pni pclmulqdq ssse3 cx16 sse4_1 sse4_2 movbe popcnt aes xsave rdrand hypervisor lahf_lm abm pti fsgsbase bmi1 smep bmi2 erms adx smap xsaveopt arat bugs : cpu_meltdown spectre_v1 spectre_v2 spec_store_bypass l1tf mds swapgs itlb_multihit srbds bogomips : 6787.28 clflush size : 64 cache_alignment : 64 address sizes : 40 bits physical, 48 bits virtual power management: processor : 1 vendor_id : GenuineIntel cpu family : 6 model : 61 model name : Intel Core Processor (Broadwell, IBRS) stepping : 2 microcode : 0x1 cpu MHz : 3393.641 cache size : 16384 KB physical id : 1 siblings : 1 core id : 0 cpu cores : 1 apicid : 1 initial apicid : 1 fpu : yes fpu_exception : yes cpuid level : 13 wp : yes flags : fpu de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 syscall nx rdtscp lm constant_tsc rep_good nopl xtopology cpuid pni pclmulqdq ssse3 cx16 sse4_1 sse4_2 movbe popcnt aes xsave rdrand hypervisor lahf_lm abm pti fsgsbase bmi1 smep bmi2 erms adx smap xsaveopt arat bugs : cpu_meltdown spectre_v1 spectre_v2 spec_store_bypass l1tf mds swapgs itlb_multihit srbds bogomips : 7096.27 clflush size : 64 cache_alignment : 64 address sizes : 40 bits physical, 48 bits virtual power management:
Now, the vendor_id is GenuineIntel not the AuthenticAMD as the host’s vendor.
TIP 1) Disable certain CPU flags (instruction sets)
As you can see with the above CPU options you can hide your exact type of processor and you could disable specific CPU flags (instruction sets) to the user’s virtual machine. The purpose is up to the user and one reason for example could be not to offer “avx” (or “avx2“) and to discourage crypto mining with the virtual machine. Or limit the SSE2/3/4/4.2/SSSE3 and other “multimedia” instruction sets to discourage video encoding and so on. Probably you would like to be used It’s up to you what to offer to the virtual machine user.
Here is the command to emulate the host CPU with all supported flags but disable “sse4.1” and “sse4.2”:
The syntax:
-cpu host,-sse4.1,-sse4.2
And the qemu command is:
qemu-system-x86_64 -enable-kvm \ -cpu host,-sse4.1,-sse4.2 \ -smp 2,maxcpus=8 \ -daemonize -vnc 192.168.0.10:1 \ -drive file=/mnt/storage/qemu/roofs/srv_virt.qcow2,index=0,cache=none,aio=threads,if=virtio \ -cdrom /mnt/storage/images/install-amd64-minimal-20140327.iso -boot d \ -net nic,model=virtio,macaddr=$(< /sys/class/net/macvtap0/address) \ -net tap,fd=3 3<>/dev/tap$(< /sys/class/net/macvtap0/ifindex) \ -balloon virtio -m 8192 \ -monitor telnet:127.0.0.1:5801,server,nowait -writeconfig /opt/qemu/config/srv_virt.qcow2.conf
So the virtual machine lacks the disabled flags. Here are the guest system flags reported by the Linux OS (with missing –sse4.1 and sse4.2):
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 syscall nx mmxext fxsr_opt pdpe1gb rdtscp lm rep_good nopl cpuid extd_apicid tsc_known_freq pni pclmulqdq ssse3 fma cx16 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand hypervisor lahf_lm cmp_legacy svm cr8_legacy abm sse4a misalignsse 3dnowprefetch osvw perfctr_core ssbd ibpb vmmcall fsgsbase tsc_adjust bmi1 avx2 smep bmi2 rdseed adx smap clflushopt sha_ni xsaveopt xsavec xgetbv1 xsaves clzero xsaveerptr virt_ssbd arat npt nrip_save arch_capabilities
The host CPU is AMD Ryzen Threadripper 1950X 16-Core Processor with flags:
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 nonstop_tsc cpuid extd_apicid amd_dcm aperfmperf pni pclmulqdq monitor ssse3 fma cx16 sse4_1 sse4_2 movbe popcnt aes xsave avx f16c rdrand lahf_lm cmp_legacy svm extapic cr8_legacy abm sse4a misalignsse 3dnowprefetch osvw skinit wdt tce topoext perfctr_core perfctr_nb bpext perfctr_llc mwaitx cpb hw_pstate sme ssbd sev ibpb vmmcall fsgsbase bmi1 avx2 smep bmi2 rdseed adx smap clflushopt sha_ni xsaveopt xsavec xgetbv1 xsaves clzero irperf xsaveerptr arat npt lbrv svm_lock nrip_save tsc_scale vmcb_clean flushbyasid decodeassists pausefilter pfthreshold avic v_vmsave_vmload vgif overflow_recov succor smca
TIP 2) Number of virtual processors in the virtual machine
The syntax -smp 2,maxcpus=8 of the qemu command will start up the virtual machine with 2 processors and you can hot add a CPU up to 8 total at any time you want with the management console listening on 127.0.0.1:5801:
qemu-system-x86_64 -enable-kvm -cpu host,-sse4.1,-sse4.2 -smp 2,maxcpus=8 \ -daemonize -vnc 192.168.0.15:1 -drive file=/srv/qemu/test/test.qcow2,index=0,cache=none,aio=threads,if=virtio \ -cdrom /srv/qemu/test/install-amd64-minimal-20201227T214503Z.iso -boot d \ -m 8192 -net nic,model=virtio,macaddr=e6:2b:b3:40:81:0c -net tap,ifname=tap0,script=no,downscript=no \ -monitor telnet:127.0.0.1:5801,server,nowait -writeconfig /srv/qemu/test/test.qcow2.conf