Provided by: qemu-system-common_6.2+dfsg-2ubuntu6.24_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