Re: [RFC PATCH] x86/cpufeatures: Enumerate new AVX512 bfloat16 instructions

[Sean Christopherson]

On Wed, Jun 12, 2019 at 06:02:59AM +0200, Borislav Petkov wrote:
> On Tue, Jun 11, 2019 at 08:32:59PM -0700, Fenghua Yu wrote:
> > Currently KVM doesn't simulate scattered features (the ones in CPUID_LNX_*
> > in cpuid_leafs) as reverse_cpuid[] doesn't contain CPUID_LNX_*.
> 
> 43500e6f294d ("x86/cpufeatures: Remove get_scattered_cpuid_leaf()")
> 
> > After the X86_FEATURES_CQM_* features are changed to scattered features,
> > they will not be simulated by KVM any more as CPUID_F_0_EDX and CPUID_F_1_EDX
> > are removed.
> 
> Does KVM even support resctrl? I doubt only exporting a couple of CPUID
> bits into the guest is enough...

KVM doesn't support resctrl.  Moving X86_FEATURES_CQM_* to a scattered
leaf won't affect KVM.

> > Should patch #1 simulate X86_FEATURE_CQM_* in KVM? Or let KVM guys handle
> > the scattered features?
> 
> Right, the scattered thing was removed as KVM didn't need it,
> apparently, see above.

Let KVM people deal with it, in the unlikely event someone adds resctrl
support to KVM.