[RFC 07/10] i386/cpu: Add a "cpuid-0x1f" property

[Zhao Liu <zhao1.liu@intel.com>]

From: Manish Mishra <manish.mishra@nutanix.com>

Add a "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
experience problems in the Guest due to the lack of 0x1f [*]. In
summary, adding 0x1f is also intended to further emulate the Host CPU
environment. Therefore, the "x-" prefix is not added to this property.

[*]: https://lore.kernel.org/qemu-devel/PH0PR02MB738410511BF51B12DB09BE6CF6AC2@PH0PR02MB7384.namprd02.prod.outlook.com/

Co-authored-by: Xiaoyao Li <xiaoyao.li@intel.com>
(Missing signed-off from Manish & Xiaoyao)
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]. Although the target cases are not exactly the same
as this patch, add the authorship of previous authors.

[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/
---
 target/i386/cpu.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index e0716dbe5934..26dc5b6a6a8c 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -9195,6 +9195,7 @@ 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("cpuid-0x1f", X86CPU, enable_cpuid_0x1f, false),
 };
 
 #ifndef CONFIG_USER_ONLY
-- 
2.34.1