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

[Zhao Liu]

On Mon, Aug 12, 2024 at 11:31:45PM -0400, Xiaoyao Li wrote:
> Date: Mon, 12 Aug 2024 23:31:45 -0400
> From: Xiaoyao Li <xiaoyao.li@intel.com>
> Subject: [PATCH v2] i386/cpu: Introduce enable_cpuid_0x1f to force exposing
>  CPUID 0x1f
> X-Mailer: git-send-email 2.34.1
> 
> 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].
> 
> Introduce a bool flag, enable_cpuid_0x1f, in CPU for the cases that
> require CPUID leaf 0x1f to be exposed to guest. For case 2), introduce
> a user settable property, "x-cpuid-0x1f" ,as well, which provides an opt-in
> interface for people to run the buggy Windows as a workaround. The default
> value of the property is set to false, thus making no effect on existing
> setup.
> 
> Introduce a new function x86_has_cpuid_0x1f(), which is the warpper of
> cpu->enable_cpuid_0x1f and x86_has_extended_topo() to check if it needs
> to enable cpuid leaf 0x1f for the guest.
> 
> [1] 
> https://lore.kernel.org/qemu-devel/20240724075226.212882-1-manish.mishra@nutanix.com/
> 
> Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
> ---
> changes in v2:
>  - Add more details in commit message;
>  - introduce a separate function x86_has_cpuid_0x1f() instead of
>    modifying x86_has_extended_topo();
> ---
>  target/i386/cpu.c     | 5 +++--
>  target/i386/cpu.h     | 9 +++++++++
>  target/i386/kvm/kvm.c | 2 +-
>  3 files changed, 13 insertions(+), 3 deletions(-)

This wrapper x86_has_cpuid_0x1f() looks good for me.

Reviewed-by: Zhao Liu <zhao1.liu@intel.com>