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)]
Reviewed-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Tested-by: Yi Lai <yi1.lai@intel.com>
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
Link: https://lore.kernel.org/r/20250711104603.1634832-6-zhao1.liu@intel.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 target/i386/cpu.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 40f3b5eac88..482979a4437 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -9940,6 +9940,7 @@ 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
-- 
2.50.0