Re: [PATCH v2] i386/cpu: Introduce enable_cpuid_0x1f to force exposing CPUID 0x1f

[Xiaoyao Li]

On 8/13/2024 10:51 PM, Xiaoyao Li wrote:
> On 8/13/2024 5:27 PM, Igor Mammedov wrote:
> > On Mon, 12 Aug 2024 23:31:45 -0400
> > Xiaoyao Li <xiaoyao.li@intel.com> wrote:
> >
> > > Currently, QEMU exposes CPUID 0x1f to guest only when necessary, i.e.,
> > > when topology level that cannot be enumerated by leaf 0xB, e.g., die or
> > > module level, are configured for the guest, e.g., -smp xx,dies=2.
> > >
> > > However, 1) TDX architecture forces to require CPUID 0x1f to 
> > > configure CPU
> > > topology. and 2) There is a bug in Windows that Windows 10/11 expects 
> > > valid
> > > 0x1f leafs when the maximum basic leaf > 0x1f[1].
> >   1. will it boot if you use older cpu model?
>
> It can boot with any cpu model that has .level < 0x1f.

I realize just now that we don't need to introduce "x-cpuid-1f" as the 
workaround for buggy windows. We can always workaround it by limiting 
the maximum basic CPUID leaf to less than 0x1f, i.e., -cpu xxx,level=0x1e

I think we can ignore this patch for now. I will re-submit it with TDX 
enabling series, and with "x-cpuid-1f" interface removed.

> >   2. how user would know that this option would be needed?
>
> Honestly, I don't have an answer for it.
>
> I'm not sure if it is the duty of QEMU to identify this case and print 
> some hint to user. It's the bug of Windows, maybe Mircosoft should put 
> something in their known bugs list for users?