Provided by: qemu-system-common_8.2.2+ds-0ubuntu1.5_amd64 
NAME
qemu-cpu-models - QEMU CPU Models
SYNOPSIS
QEMU CPU Modelling Infrastructure manual
DESCRIPTION
Recommendations for KVM CPU model configuration on x86 hosts
The information that follows provides recommendations for configuring CPU models on x86 hosts. The goals
are to maximise performance, while protecting guest OS against various CPU hardware flaws, and optionally
enabling live migration between hosts with heterogeneous CPU models.
Two ways to configure CPU models with QEMU / KVM
1. Host passthrough
This passes the host CPU model features, model, stepping, exactly to the guest. Note that KVM may
filter out some host CPU model features if they cannot be supported with virtualization. Live
migration is unsafe when this mode is used as libvirt / QEMU cannot guarantee a stable CPU is exposed
to the guest across hosts. This is the recommended CPU to use, provided live migration is not
required.
2. Named model
QEMU comes with a number of predefined named CPU models, that typically refer to specific generations
of hardware released by Intel and AMD. These allow the guest VMs to have a degree of isolation from
the host CPU, allowing greater flexibility in live migrating between hosts with differing hardware.
@end table
In both cases, it is possible to optionally add or remove individual CPU features, to alter what is
presented to the guest by default.
Libvirt supports a third way to configure CPU models known as "Host model". This uses the QEMU "Named
model" feature, automatically picking a CPU model that is similar the host CPU, and then adding extra
features to approximate the host model as closely as possible. This does not guarantee the CPU family,
stepping, etc will precisely match the host CPU, as they would with "Host passthrough", but gives much of
the benefit of passthrough, while making live migration safe.
ABI compatibility levels for CPU models
The x86_64 architecture has a number of ABI compatibility levels defined. Traditionally most operating
systems and toolchains would only target the original baseline ABI. It is expected that in future OS and
toolchains are likely to target newer ABIs. The table that follows illustrates which ABI compatibility
levels can be satisfied by the QEMU CPU models. Note that the table only lists the long term stable CPU
model versions (eg Haswell-v4). In addition to what is listed, there are also many CPU model aliases
which resolve to a different CPU model version, depending on the machine type is in use.
x86-64 ABI compatibility levels
┌──────────────────────┬──────────┬────┬────┬────┐
│Model │ baseline │ v2 │ v3 │ v4 │
├──────────────────────┼──────────┼────┼────┼────┤
│486-v1 │ │ │ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│Broadwell-v1 │ ✅ │ ✅ │ ✅ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│Broadwell-v2 │ ✅ │ ✅ │ ✅ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│Broadwell-v3 │ ✅ │ ✅ │ ✅ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│Broadwell-v4 │ ✅ │ ✅ │ ✅ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│Cascadelake-Server-v1 │ ✅ │ ✅ │ ✅ │ ✅ │
└──────────────────────┴──────────┴────┴────┴────┘
│Cascadelake-Server-v2 │ ✅ │ ✅ │ ✅ │ ✅ │
├──────────────────────┼──────────┼────┼────┼────┤
│Cascadelake-Server-v3 │ ✅ │ ✅ │ ✅ │ ✅ │
├──────────────────────┼──────────┼────┼────┼────┤
│Cascadelake-Server-v4 │ ✅ │ ✅ │ ✅ │ ✅ │
├──────────────────────┼──────────┼────┼────┼────┤
│Conroe-v1 │ ✅ │ │ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│Cooperlake-v1 │ ✅ │ ✅ │ ✅ │ ✅ │
├──────────────────────┼──────────┼────┼────┼────┤
│Denverton-v1 │ ✅ │ ✅ │ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│Denverton-v2 │ ✅ │ ✅ │ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│Dhyana-v1 │ ✅ │ ✅ │ ✅ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│EPYC-Milan-v1 │ ✅ │ ✅ │ ✅ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│EPYC-Rome-v1 │ ✅ │ ✅ │ ✅ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│EPYC-Rome-v2 │ ✅ │ ✅ │ ✅ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│EPYC-v1 │ ✅ │ ✅ │ ✅ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│EPYC-v2 │ ✅ │ ✅ │ ✅ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│EPYC-v3 │ ✅ │ ✅ │ ✅ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│Haswell-v1 │ ✅ │ ✅ │ ✅ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│Haswell-v2 │ ✅ │ ✅ │ ✅ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│Haswell-v3 │ ✅ │ ✅ │ ✅ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│Haswell-v4 │ ✅ │ ✅ │ ✅ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│Icelake-Client-v1 │ ✅ │ ✅ │ ✅ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│Icelake-Client-v2 │ ✅ │ ✅ │ ✅ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│Icelake-Server-v1 │ ✅ │ ✅ │ ✅ │ ✅ │
├──────────────────────┼──────────┼────┼────┼────┤
│Icelake-Server-v2 │ ✅ │ ✅ │ ✅ │ ✅ │
├──────────────────────┼──────────┼────┼────┼────┤
│Icelake-Server-v3 │ ✅ │ ✅ │ ✅ │ ✅ │
├──────────────────────┼──────────┼────┼────┼────┤
│Icelake-Server-v4 │ ✅ │ ✅ │ ✅ │ ✅ │
├──────────────────────┼──────────┼────┼────┼────┤
│IvyBridge-v1 │ ✅ │ ✅ │ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│IvyBridge-v2 │ ✅ │ ✅ │ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│KnightsMill-v1 │ ✅ │ ✅ │ ✅ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│Nehalem-v1 │ ✅ │ ✅ │ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│Nehalem-v2 │ ✅ │ ✅ │ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│Opteron_G1-v1 │ ✅ │ │ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│Opteron_G2-v1 │ ✅ │ │ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│Opteron_G3-v1 │ ✅ │ │ │ │
└──────────────────────┴──────────┴────┴────┴────┘
│Opteron_G4-v1 │ ✅ │ ✅ │ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│Opteron_G5-v1 │ ✅ │ ✅ │ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│Penryn-v1 │ ✅ │ │ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│SandyBridge-v1 │ ✅ │ ✅ │ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│SandyBridge-v2 │ ✅ │ ✅ │ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│Skylake-Client-v1 │ ✅ │ ✅ │ ✅ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│Skylake-Client-v2 │ ✅ │ ✅ │ ✅ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│Skylake-Client-v3 │ ✅ │ ✅ │ ✅ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│Skylake-Server-v1 │ ✅ │ ✅ │ ✅ │ ✅ │
├──────────────────────┼──────────┼────┼────┼────┤
│Skylake-Server-v2 │ ✅ │ ✅ │ ✅ │ ✅ │
├──────────────────────┼──────────┼────┼────┼────┤
│Skylake-Server-v3 │ ✅ │ ✅ │ ✅ │ ✅ │
├──────────────────────┼──────────┼────┼────┼────┤
│Skylake-Server-v4 │ ✅ │ ✅ │ ✅ │ ✅ │
├──────────────────────┼──────────┼────┼────┼────┤
│Snowridge-v1 │ ✅ │ ✅ │ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│Snowridge-v2 │ ✅ │ ✅ │ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│Westmere-v1 │ ✅ │ ✅ │ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│Westmere-v2 │ ✅ │ ✅ │ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│athlon-v1 │ │ │ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│core2duo-v1 │ ✅ │ │ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│coreduo-v1 │ │ │ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│kvm32-v1 │ │ │ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│kvm64-v1 │ ✅ │ │ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│n270-v1 │ │ │ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│pentium-v1 │ │ │ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│pentium2-v1 │ │ │ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│pentium3-v1 │ │ │ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│phenom-v1 │ ✅ │ │ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│qemu32-v1 │ │ │ │ │
├──────────────────────┼──────────┼────┼────┼────┤
│qemu64-v1 │ ✅ │ │ │ │
└──────────────────────┴──────────┴────┴────┴────┘
Preferred CPU models for Intel x86 hosts
The following CPU models are preferred for use on Intel hosts. Administrators / applications are
recommended to use the CPU model that matches the generation of the host CPUs in use. In a deployment
with a mixture of host CPU models between machines, if live migration compatibility is required, use the
newest CPU model that is compatible across all desired hosts.
Cascadelake-Server, Cascadelake-Server-noTSX
Intel Xeon Processor (Cascade Lake, 2019), with "stepping" levels 6 or 7 only. (The Cascade Lake
Xeon processor with stepping 5 is vulnerable to MDS variants.)
Skylake-Server, Skylake-Server-IBRS, Skylake-Server-IBRS-noTSX
Intel Xeon Processor (Skylake, 2016)
Skylake-Client, Skylake-Client-IBRS, Skylake-Client-noTSX-IBRS}
Intel Core Processor (Skylake, 2015)
Broadwell, Broadwell-IBRS, Broadwell-noTSX, Broadwell-noTSX-IBRS
Intel Core Processor (Broadwell, 2014)
Haswell, Haswell-IBRS, Haswell-noTSX, Haswell-noTSX-IBRS
Intel Core Processor (Haswell, 2013)
IvyBridge, IvyBridge-IBR
Intel Xeon E3-12xx v2 (Ivy Bridge, 2012)
SandyBridge, SandyBridge-IBRS
Intel Xeon E312xx (Sandy Bridge, 2011)
Westmere, Westmere-IBRS
Westmere E56xx/L56xx/X56xx (Nehalem-C, 2010)
Nehalem, Nehalem-IBRS
Intel Core i7 9xx (Nehalem Class Core i7, 2008)
Penryn Intel Core 2 Duo P9xxx (Penryn Class Core 2, 2007)
Conroe Intel Celeron_4x0 (Conroe/Merom Class Core 2, 2006)
Important CPU features for Intel x86 hosts
The following are important CPU features that should be used on Intel x86 hosts, when available in the
host CPU. Some of them require explicit configuration to enable, as they are not included by default in
some, or all, of the named CPU models listed above. In general all of these features are included if
using "Host passthrough" or "Host model".
pcid Recommended to mitigate the cost of the Meltdown (CVE-2017-5754) fix.
Included by default in Haswell, Broadwell & Skylake Intel CPU models.
Should be explicitly turned on for Westmere, SandyBridge, and IvyBridge Intel CPU models. Note
that some desktop/mobile Westmere CPUs cannot support this feature.
spec-ctrl
Required to enable the Spectre v2 (CVE-2017-5715) fix.
Included by default in Intel CPU models with -IBRS suffix.
Must be explicitly turned on for Intel CPU models without -IBRS suffix.
Requires the host CPU microcode to support this feature before it can be used for guest CPUs.
stibp Required to enable stronger Spectre v2 (CVE-2017-5715) fixes in some operating systems.
Must be explicitly turned on for all Intel CPU models.
Requires the host CPU microcode to support this feature before it can be used for guest CPUs.
ssbd Required to enable the CVE-2018-3639 fix.
Not included by default in any Intel CPU model.
Must be explicitly turned on for all Intel CPU models.
Requires the host CPU microcode to support this feature before it can be used for guest CPUs.
pdpe1gb
Recommended to allow guest OS to use 1GB size pages.
Not included by default in any Intel CPU model.
Should be explicitly turned on for all Intel CPU models.
Note that not all CPU hardware will support this feature.
md-clear
Required to confirm the MDS (CVE-2018-12126, CVE-2018-12127, CVE-2018-12130, CVE-2019-11091)
fixes.
Not included by default in any Intel CPU model.
Must be explicitly turned on for all Intel CPU models.
Requires the host CPU microcode to support this feature before it can be used for guest CPUs.
mds-no Recommended to inform the guest OS that the host is not vulnerable to any of the MDS variants
([MFBDS] CVE-2018-12130, [MLPDS] CVE-2018-12127, [MSBDS] CVE-2018-12126).
This is an MSR (Model-Specific Register) feature rather than a CPUID feature, so it will not
appear in the Linux /proc/cpuinfo in the host or guest. Instead, the host kernel uses it to
populate the MDS vulnerability file in sysfs.
So it should only be enabled for VMs if the host reports @code{Not affected} in the
/sys/devices/system/cpu/vulnerabilities/mds file.
taa-no Recommended to inform that the guest that the host is not vulnerable to CVE-2019-11135, TSX
Asynchronous Abort (TAA).
This too is an MSR feature, so it does not show up in the Linux /proc/cpuinfo in the host or
guest.
It should only be enabled for VMs if the host reports Not affected in the
/sys/devices/system/cpu/vulnerabilities/tsx_async_abort file.
tsx-ctrl
Recommended to inform the guest that it can disable the Intel TSX (Transactional Synchronization
Extensions) feature; or, if the processor is vulnerable, use the Intel VERW instruction (a
processor-level instruction that performs checks on memory access) as a mitigation for the TAA
vulnerability. (For details, refer to Intel's deep dive into MDS.)
Expose this to the guest OS if and only if: (a) the host has TSX enabled; and (b) the guest has
rtm CPU flag enabled.
By disabling TSX, KVM-based guests can avoid paying the price of mitigating TSX-based attacks.
Note that tsx-ctrl too is an MSR feature, so it does not show up in the Linux /proc/cpuinfo in the
host or guest.
To validate that Intel TSX is indeed disabled for the guest, there are two ways: (a) check for the
absence of rtm in the guest's /proc/cpuinfo; or (b) the
/sys/devices/system/cpu/vulnerabilities/tsx_async_abort file in the guest should report
Mitigation: TSX disabled.
Preferred CPU models for AMD x86 hosts
The following CPU models are preferred for use on AMD hosts. Administrators / applications are
recommended to use the CPU model that matches the generation of the host CPUs in use. In a deployment
with a mixture of host CPU models between machines, if live migration compatibility is required, use the
newest CPU model that is compatible across all desired hosts.
EPYC, EPYC-IBPB
AMD EPYC Processor (2017)
Opteron_G5
AMD Opteron 63xx class CPU (2012)
Opteron_G4
AMD Opteron 62xx class CPU (2011)
Opteron_G3
AMD Opteron 23xx (Gen 3 Class Opteron, 2009)
Opteron_G2
AMD Opteron 22xx (Gen 2 Class Opteron, 2006)
Opteron_G1
AMD Opteron 240 (Gen 1 Class Opteron, 2004)
Important CPU features for AMD x86 hosts
The following are important CPU features that should be used on AMD x86 hosts, when available in the host
CPU. Some of them require explicit configuration to enable, as they are not included by default in some,
or all, of the named CPU models listed above. In general all of these features are included if using
"Host passthrough" or "Host model".
ibpb Required to enable the Spectre v2 (CVE-2017-5715) fix.
Included by default in AMD CPU models with -IBPB suffix.
Must be explicitly turned on for AMD CPU models without -IBPB suffix.
Requires the host CPU microcode to support this feature before it can be used for guest CPUs.
stibp Required to enable stronger Spectre v2 (CVE-2017-5715) fixes in some operating systems.
Must be explicitly turned on for all AMD CPU models.
Requires the host CPU microcode to support this feature before it can be used for guest CPUs.
virt-ssbd
Required to enable the CVE-2018-3639 fix
Not included by default in any AMD CPU model.
Must be explicitly turned on for all AMD CPU models.
This should be provided to guests, even if amd-ssbd is also provided, for maximum guest
compatibility.
Note for some QEMU / libvirt versions, this must be force enabled when when using "Host model",
because this is a virtual feature that doesn't exist in the physical host CPUs.
amd-ssbd
Required to enable the CVE-2018-3639 fix
Not included by default in any AMD CPU model.
Must be explicitly turned on for all AMD CPU models.
This provides higher performance than virt-ssbd so should be exposed to guests whenever available
in the host. virt-ssbd should none the less also be exposed for maximum guest compatibility as
some kernels only know about virt-ssbd.
amd-no-ssb
Recommended to indicate the host is not vulnerable CVE-2018-3639
Not included by default in any AMD CPU model.
Future hardware generations of CPU will not be vulnerable to CVE-2018-3639, and thus the guest
should be told not to enable its mitigations, by exposing amd-no-ssb. This is mutually exclusive
with virt-ssbd and amd-ssbd.
pdpe1gb
Recommended to allow guest OS to use 1GB size pages
Not included by default in any AMD CPU model.
Should be explicitly turned on for all AMD CPU models.
Note that not all CPU hardware will support this feature.
Default x86 CPU models
The default QEMU CPU models are designed such that they can run on all hosts. If an application does not
wish to do perform any host compatibility checks before launching guests, the default is guaranteed to
work.
The default CPU models will, however, leave the guest OS vulnerable to various CPU hardware flaws, so
their use is strongly discouraged. Applications should follow the earlier guidance to setup a better CPU
configuration, with host passthrough recommended if live migration is not needed.
qemu32, qemu64
QEMU Virtual CPU version 2.5+ (32 & 64 bit variants)
qemu64 is used for x86_64 guests and qemu32 is used for i686 guests, when no -cpu argument is given to
QEMU, or no <cpu> is provided in libvirt XML.
Other non-recommended x86 CPUs
The following CPUs models are compatible with most AMD and Intel x86 hosts, but their usage is
discouraged, as they expose a very limited featureset, which prevents guests having optimal performance.
kvm32, kvm64
Common KVM processor (32 & 64 bit variants).
Legacy models just for historical compatibility with ancient QEMU versions.
486, athlon, phenom, coreduo, core2duo, n270, pentium, pentium2, pentium3
Various very old x86 CPU models, mostly predating the introduction of hardware assisted
virtualization, that should thus not be required for running virtual machines.
Syntax for configuring CPU models
The examples below illustrate the approach to configuring the various CPU models / features in QEMU and
libvirt.
QEMU command line
Host passthrough:
qemu-system-x86_64 -cpu host
Host passthrough with feature customization:
qemu-system-x86_64 -cpu host,vmx=off,...
Named CPU models:
qemu-system-x86_64 -cpu Westmere
Named CPU models with feature customization:
qemu-system-x86_64 -cpu Westmere,pcid=on,...
Libvirt guest XML
Host passthrough:
<cpu mode='host-passthrough'/>
Host passthrough with feature customization:
<cpu mode='host-passthrough'>
<feature name="vmx" policy="disable"/>
...
</cpu>
Host model:
<cpu mode='host-model'/>
Host model with feature customization:
<cpu mode='host-model'>
<feature name="vmx" policy="disable"/>
...
</cpu>
Named model:
<cpu mode='custom'>
<model name="Westmere"/>
</cpu>
Named model with feature customization:
<cpu mode='custom'>
<model name="Westmere"/>
<feature name="pcid" policy="require"/>
...
</cpu>
Supported CPU model configurations on MIPS hosts
QEMU supports variety of MIPS CPU models:
Supported CPU models for MIPS32 hosts
The following CPU models are supported for use on MIPS32 hosts. Administrators / applications are
recommended to use the CPU model that matches the generation of the host CPUs in use. In a deployment
with a mixture of host CPU models between machines, if live migration compatibility is required, use the
newest CPU model that is compatible across all desired hosts.
mips32r6-generic
MIPS32 Processor (Release 6, 2015)
P5600 MIPS32 Processor (P5600, 2014)
M14K, M14Kc
MIPS32 Processor (M14K, 2009)
74Kf MIPS32 Processor (74K, 2007)
34Kf MIPS32 Processor (34K, 2006)
24Kc, 24KEc, 24Kf
MIPS32 Processor (24K, 2003)
4Kc, 4Km, 4KEcR1, 4KEmR1, 4KEc, 4KEm
MIPS32 Processor (4K, 1999)
Supported CPU models for MIPS64 hosts
The following CPU models are supported for use on MIPS64 hosts. Administrators / applications are
recommended to use the CPU model that matches the generation of the host CPUs in use. In a deployment
with a mixture of host CPU models between machines, if live migration compatibility is required, use the
newest CPU model that is compatible across all desired hosts.
I6400 MIPS64 Processor (Release 6, 2014)
Loongson-2E
MIPS64 Processor (Loongson 2, 2006)
Loongson-2F
MIPS64 Processor (Loongson 2, 2008)
Loongson-3A1000
MIPS64 Processor (Loongson 3, 2010)
Loongson-3A4000
MIPS64 Processor (Loongson 3, 2018)
mips64dspr2
MIPS64 Processor (Release 2, 2006)
MIPS64R2-generic, 5KEc, 5KEf
MIPS64 Processor (Release 2, 2002)
20Kc MIPS64 Processor (20K, 2000
5Kc, 5Kf
MIPS64 Processor (5K, 1999)
VR5432 MIPS64 Processor (VR, 1998)
R4000 MIPS64 Processor (MIPS III, 1991)
Supported CPU models for nanoMIPS hosts
The following CPU models are supported for use on nanoMIPS hosts. Administrators / applications are
recommended to use the CPU model that matches the generation of the host CPUs in use. In a deployment
with a mixture of host CPU models between machines, if live migration compatibility is required, use the
newest CPU model that is compatible across all desired hosts.
I7200 MIPS I7200 (nanoMIPS, 2018)
Preferred CPU models for MIPS hosts
The following CPU models are preferred for use on different MIPS hosts:
MIPS III
R4000
MIPS32R2
34Kf
MIPS64R6
I6400
nanoMIPS
I7200
SEE ALSO
The HTML documentation of QEMU for more precise information and Linux user mode emulator invocation.
AUTHOR
The QEMU Project developers
COPYRIGHT
2024, The QEMU Project Developers