[Bug 54471] New: nVMX: TRUE* MSRs unnecessary

[Bug 54471] New: nVMX: TRUE* MSRs unnecessary

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=54471

           Summary: nVMX: TRUE* MSRs unnecessary
           Product: Virtualization
           Version: unspecified
          Platform: All
        OS/Version: Linux
              Tree: Mainline
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: kvm
        AssignedTo: virtualization_kvm@kernel-bugs.osdl.org
        ReportedBy: nyh@math.technion.ac.il
        Regression: No


According to the spec, the TRUE* MSRs are only necessary if bit 55 of VMX_BASIC
is on. Since we don't set this bit, we don't need to provide these MSRs...
So probably we shouldn't.

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[Bug 54471] nVMX: TRUE* MSRs unnecessary

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=54471


Nadav Har'El <nyh@math.technion.ac.il> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Blocks|                            |53601




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Re: [Bug 54471] New: nVMX: TRUE* MSRs unnecessary

[Jan Kiszka]

On 2013-02-25 15:04, bugzilla-daemon@bugzilla.kernel.org wrote:
> https://bugzilla.kernel.org/show_bug.cgi?id=54471
> 
>            Summary: nVMX: TRUE* MSRs unnecessary
>            Product: Virtualization
>            Version: unspecified
>           Platform: All
>         OS/Version: Linux
>               Tree: Mainline
>             Status: NEW
>           Severity: enhancement
>           Priority: P1
>          Component: kvm
>         AssignedTo: virtualization_kvm@kernel-bugs.osdl.org
>         ReportedBy: nyh@math.technion.ac.il
>         Regression: No
> 
> 
> According to the spec, the TRUE* MSRs are only necessary if bit 55 of VMX_BASIC
> is on. Since we don't set this bit, we don't need to provide these MSRs...
> So probably we shouldn't.

I tend to say we should (i.e. set bit 55) as there is the risk that
buggy guests could needlessly get confused when we expose very recent
features (like EPT) and do not provide such "old-fashioned" stuff.

Jan

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[Bug 54471] nVMX: TRUE* MSRs unnecessary

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=54471





--- Comment #1 from Anonymous Emailer <anonymous@kernel-bugs.osdl.org>  2013-02-25 14:29:08 ---
Reply-To: jan.kiszka@siemens.com

On 2013-02-25 15:04, bugzilla-daemon@bugzilla.kernel.org wrote:
> https://bugzilla.kernel.org/show_bug.cgi?id=54471
> 
>            Summary: nVMX: TRUE* MSRs unnecessary
>            Product: Virtualization
>            Version: unspecified
>           Platform: All
>         OS/Version: Linux
>               Tree: Mainline
>             Status: NEW
>           Severity: enhancement
>           Priority: P1
>          Component: kvm
>         AssignedTo: virtualization_kvm@kernel-bugs.osdl.org
>         ReportedBy: nyh@math.technion.ac.il
>         Regression: No
> 
> 
> According to the spec, the TRUE* MSRs are only necessary if bit 55 of VMX_BASIC
> is on. Since we don't set this bit, we don't need to provide these MSRs...
> So probably we shouldn't.

I tend to say we should (i.e. set bit 55) as there is the risk that
buggy guests could needlessly get confused when we expose very recent
features (like EPT) and do not provide such "old-fashioned" stuff.

Jan

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[Bug 54471] nVMX: TRUE* MSRs unnecessary

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=54471

Bandan Das <bsd@makefile.in> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Blocks|                            |94971

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[Bug 54471] nVMX: TRUE* MSRs unnecessary

[bugzilla-daemon]

https://bugzilla.kernel.org/show_bug.cgi?id=54471

Paolo Bonzini <bonzini@gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |bonzini@gnu.org
     Kernel Version|                            |3.19
         Resolution|---                         |INVALID

--- Comment #2 from Paolo Bonzini <bonzini@gnu.org> ---
TRUE_* is needed to tell the guest that it can disable CR3 load/store exits. 
We were enabling this control by exposing a broken MSR_IA32_VMX_PROCBASED_CTLS
value, but commit 560b7ee12ca5 (KVM: nVMX: Fix returned value of
MSR_IA32_VMX_PROCBASED_CTLS, 2014-06-16).  So we can no longer remove the
TRUE_* MSRs.

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