[Qemu-devel] Cascadelake-Server missing MSR based features ?

[Daniel P . Berrangé]

The Cascadelake-Server CPU was added last year in

  commit c7a88b52f62b30c04158eeb07f73e3f72221b6a8
  Author: Tao Xu <address@hidden>
  Date:   Wed Sep 19 11:11:22 2018 +0800

    i386: Add new model of Cascadelake-Server

The commit message says that MSR based features are initially
omitted from its definition:

  [quote]
    On Cascadelake, some capabilities (RDCL_NO, IBRS_ALL, RSBA,
    SKIP_L1DFL_VMENTRY and SSB_NO) are enumerated by MSR.
    These features rely on MSR based feature support patch.
    Will be added later after that patch's in.
    http://lists.nongnu.org/archive/html/qemu-devel/2018-09/msg00074.html
  [/quote]

The commits referenced in that URL, however, were merged *before*
this Cascadelake-Server CPU was merged in QEMU:

  commit d86f963694df27f11b3681ffd225c9362de1b634
  Author: Robert Hoo <address@hidden>
  Date:   Mon Oct 15 12:47:25 2018 +0800

    x86: define a new MSR based feature word -- FEATURE_WORDS_ARCH_CAPABILITIES

  commit 07585923485952bf4cb7da563c9f91fecc85d09c
  Author: Robert Hoo <address@hidden>
  Date:   Mon Oct 15 12:47:24 2018 +0800

    x86: Data structure changes to support MSR based features
    
  commit f57bceb6ab5163ddd6c41ff4344ab8cf28a9c63d
  Author: Robert Hoo <address@hidden>
  Date:   Mon Oct 15 12:47:23 2018 +0800

    kvm: Add support to KVM_GET_MSR_FEATURE_INDEX_LIST and KVM_GET_MSRS system 
ioctl
    

None the less, the Cascadelake-Server CPU in QEMU still does not appear
to have the  RDCL_NO, IBRS_ALL, RSBA, SKIP_L1DFL_VMENTRY and SSB_NO
features present (unless I'm mis-reading the codE).

I see a later commit updated the stepping supposedly to enable
the MSR based features to be exposed but still doesn't appear to have
actually exposed them:

  commit b0a1980384fc265d91de7e09aa5fe531a69e6288
  Author: Tao Xu <address@hidden>
  Date:   Thu Dec 27 10:43:03 2018 +0800

    i386: Update stepping of Cascadelake-Server
    
    Update the stepping from 5 to 6, in order that
    the Cascadelake-Server CPU model can support AVX512VNNI
    and MSR based features exposed by ARCH_CAPABILITIES.

Can anyone shed light on what the status is wrt exposing the MSR based
features in Cascadelake-Server ?

Regards,
Daniel
-- 
|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|