** Changed in: charm-nova-compute Status: Fix Committed => Fix Released
-- You received this bug notification because you are a member of Yahoo! Engineering Team, which is subscribed to OpenStack Compute (nova). https://bugs.launchpad.net/bugs/1750829 Title: RFE: libvirt: Add ability to configure extra CPU flags for named CPU models Status in OpenStack nova-compute charm: Fix Released Status in OpenStack Compute (nova): Fix Released Status in OpenStack Compute (nova) ocata series: Fix Released Status in OpenStack Compute (nova) pike series: Fix Committed Status in OpenStack Compute (nova) queens series: Fix Committed Bug description: Motivation ---------- The recent "Meltdown" CVE fixes resulted in critical performance penalty, From here[*]: [...] However, in examining both the various fixes rolled out in actual Linux distros over the past few days and doing some very informal surveying of environments I have access to, I discovered that the PCID ["process-context identifiers"] processor feature, which used to be a virtual no-op, is now a performance AND security critical item.[...] So if a Nova user has applied all the "Meltdown" CVE fixes, and is using a named CPU model (like "IvyBridge", or "Westmere" — which specifically lack the said obscure "PCID" feature) they will incur severe performance degradation[*]. Note that some of Intel *physical* CPUs themselves include the 'pcid' CPU feature flag; but the named CPU models provided by libvirt & QEMU lack that flag — hence we explicitly specify it for virtual CPUs via the following proposed config attribute. [*] https://groups.google.com/forum/m/#!topic/mechanical- sympathy/L9mHTbeQLNU Proposed change --------------- Modify Nova's libvirt driver such that it will be possible to set granular CPU feature flags for named CPU models. E.g. to explicitly specify the 'pcid' feature flag with Intel IvyBridge CPU model, set the following in /etc/nova.conf: ... [libvirt] cpu_model=IvyBridge cpu_model_extra_flags="pcid" ... The list of known CPU feature flags ('vmx', 'xtpr', 'pcid', et cetera) can be found in /usr/share/libvirt/cpu_map.xml. Note that before specifying extra CPU feature flags, one should check if the named CPU models (provided by libvirt) already include the said flags. E.g. the 'Broadwell', 'Haswell-noTSX' named CPU models provided by libvirt already provides the 'pcid' CPU feature flag. Other use cases --------------- - Nested Virtualization — an operator can specify the Intel 'vmx' or AMD 'svm' flags in the level-1 guest (i.e. the guest hypervisor) - Ability to use 1GB huge pages with Haswell model as one use case for extra flags (thanks: Daniel Berrangé, for mentioning this scenario): cpu_model_extra_flags=Haswell cpu_model_extra_flags="pdpe1gb" To manage notifications about this bug go to: https://bugs.launchpad.net/charm-nova-compute/+bug/1750829/+subscriptions -- Mailing list: https://launchpad.net/~yahoo-eng-team Post to : yahoo-eng-team@lists.launchpad.net Unsubscribe : https://launchpad.net/~yahoo-eng-team More help : https://help.launchpad.net/ListHelp