Re: [Xen-devel] [PATCH] libxc/x86: don't hand through CPUID leaf 0x80000008 as is

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 17.05.18 at 15:26, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 17/05/18 14:20, Jan Beulich wrote:
>> Just like for HVM the feature set should be used for EBX output, while
>> EAX should be restricted to the low 16 bits and ECX/EDX should be zero.
>>
>> Short of there being white listing in place just like on the HVM side,
>> also zap leaves 6, 9, and 0x80000007 as well as unknown / reserved ones.
>>
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> 
> Do you want this for backporting?

Not really, at least that wasn't a primary goal.

> The changes below are enforced by recalculate_cpuid_policy() (and in
> particular, recaluclate_misc()) in the hypervisor for the past few
> releases, and Sergey is currently in the process of making all of this
> libxc logic disappear.

Well, maybe I'm simply confused: Commit d297b56682 ("x86/cpuid: Handling
of IBRS/IBPB, STIBP and IBRS for guests") introduced similar code into
xc_cpuid_hvm_policy() without doing the same for xc_cpuid_pv_policy().
That's pretty recent a commit, and one that has been backported all the
way through to 4.6. Are you saying that was a pointless change then?

Jan



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