Re: [PATCH 0/2] KVM: x86: Propagate AMD-specific IBRS bits to guests

[Sean Christopherson]

On Tue, Feb 28, 2023, Borislav Petkov wrote:
> On Tue, Feb 28, 2023 at 10:24:16PM +0000, Takahiro Itazuri wrote:
> > I'm still a kernel newbie and I don't have a strong opinion for that.
> > I just thought it would be helpful if the KVM_GET_SUPPORTED_CPUID API
> > returns the same security information as the host, as long as it is
> > harmless.
> 
> Not harmless - cpufeatures.h should contain flags which the kernel uses
> and not *every* CPUID bit out there.

I thought that the consensus was that adding unused-by-the-kernel flags to
cpufeatures.h is ok so long as the feature is hidden from /proc/cpuinfo and the
kernel already dedicates a word to the CPUID leaf?