Re: [RESEND PATCH v3] KVM: x86: Add Intel CPUID.1F cpuid emulation support

[Like Xu]

On 2019/6/4 3:18, Sean Christopherson wrote:
> On Mon, Jun 03, 2019 at 06:56:17PM +0200, Radim KrÄmÃÅ wrote:
> > > +			break;
> > > +		}
> > >   		entry->eax = min(entry->eax, (u32)(f_intel_pt ? 0x14 : 0xd));
> >
> > Similarly in the existing code.  If we don't have f_intel_pt, then we
> > should make sure that leaf 0x14 is not being filled, but we don't really
> > have to limit the maximal index.
> >
> > Adding a single clamping like
> >
> > 		/* Limited to the highest leaf implemented in KVM. */
> > 		entry->eax = min(entry->eax, 0x1f);
> >
> > seems sufficient.
> >
> > (Passing the hardware value is ok in theory, but it is a cheap way to
> >   avoid future leaves that cannot be simply zeroed for some weird reason.)
>
> I don't have a strong opinion regarding the code itself, but whatever ends
> up getting committed should have a big beefy changelog explaining why the
> clamping exists, or at least extolling its virtues.  I had a hell of a
> time understanding the intent of this one line of code because as your
> response shows, there is no one right answer.

Hi Radim & Sean,

Thanks for your review and finally we find a better way.

Please help review the new version, I am not sure that the changelog 
could help new submitter understand why the clamping exists.