Re: [PATCH 5/8] i386/cpu: Add a "x-force-cpuid-0x1f" property

["Mi, Dapeng" <dapeng1.mi@linux.intel.com>]

On 6/26/2025 4:31 PM, Zhao Liu wrote:
> From: Manish Mishra <manish.mishra@nutanix.com>
>
> Add a "x-force-cpuid-0x1f" property so that CPU models can enable it and
> have 0x1f CPUID leaf natually as the Host CPU.
>
> The advantage is that when the CPU model's cache model is already
> consistent with the Host CPU, for example, SRF defaults to l2 per
> module & l3 per package, 0x1f can better help users identify the
> topology in the VM.
>
> Adding 0x1f for specific CPU models should not cause any trouble in
> principle. This property is only enabled for CPU models that already
> have 0x1f leaf on the Host, so software that originally runs normally on
> the Host won't encounter issues in the Guest with corresponding CPU
> model. Conversely, some software that relies on checking 0x1f might
> have problems in the Guest due to the lack of 0x1f [*]. In
> summary, adding 0x1f is also intended to further emulate the Host CPU
> environment.
>
> [*]: https://lore.kernel.org/qemu-devel/PH0PR02MB738410511BF51B12DB09BE6CF6AC2@PH0PR02MB7384.namprd02.prod.outlook.com/
>
> Signed-off-by: Manish Mishra <manish.mishra@nutanix.com>
> Co-authored-by: Xiaoyao Li <xiaoyao.li@intel.com>
> Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
> [Integrated and rebased 2 previous patches (ordered by post time)]
> Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
> ---
> Note:
>   This patch integrates the idea from 2 previous posted patches (ordered
> by post time)[1] [2], following the s-o-b policy of "Re-starting
> abandoned work" in docs/devel/code-provenance.rst.
>
> [1]: From Manish: https://lore.kernel.org/qemu-devel/20240722101859.47408-1-manish.mishra@nutanix.com/
> [2]: From Xiaoyao: https://lore.kernel.org/qemu-devel/20240813033145.279307-1-xiaoyao.li@intel.com/
> ---
> Changes since RFC:
>  * Rebase and rename the property as "x-force-cpuid-0x1f". (Igor)
> ---
>  target/i386/cpu.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index 08c84ba90f52..ee36f7ee2ccc 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -9934,6 +9934,7 @@ static const Property x86_cpu_properties[] = {
>      DEFINE_PROP_BOOL("x-intel-pt-auto-level", X86CPU, intel_pt_auto_level,
>                       true),
>      DEFINE_PROP_BOOL("x-l1-cache-per-thread", X86CPU, l1_cache_per_core, true),
> +    DEFINE_PROP_BOOL("x-force-cpuid-0x1f", X86CPU, force_cpuid_0x1f, false),
>  };
>  
>  #ifndef CONFIG_USER_ONLY

LGTM.

Reviewed-by: Dapeng Mi <dapeng1.mi@linux.intel.com>