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

[Tao Xu]

On 3/19/2019 8:16 PM, Daniel P. Berrangé wrote:
> 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 ?

Hi, I sent the patch to add the MSR based features with the Update 
stepping patch together last year, and we discussed a lot about it:

[1] https://patchwork.kernel.org/patch/10743427/

Tao