[v2 PATCH] target/i386: Fix the CPUID leaf CPUID_Fn80000008

[Babu Moger]

CPUID leaf CPUID_Fn80000008_ECX provides information about the
number of threads supported by the processor. It was found that
the field ApicIdSize(bits 15-12) was not set correctly.

ApicIdSize is defined as the number of bits required to represent
all the ApicId values within a package.

Valid Values: Value Description
3h-0h           Reserved.
4h              up to 16 threads.
5h              up to 32 threads.
6h              up to 64 threads.
7h              up to 128 threads.
Fh-8h           Reserved.

Fix the bit appropriately.

This came up during following thread.
https://lore.kernel.org/qemu-devel/address@hidden/#t

Refer the Processor Programming Reference (PPR) for AMD Family 17h
Model 01h, Revision B1 Processors. The documentation is available
from the bugzilla Link below.
Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537

Reported-by: Philipp Eppelt <address@hidden>
Signed-off-by: Babu Moger <address@hidden>
---
v2: 
  Used env->pkg_offset for bits 15:12 which is already available.

 target/i386/cpu.c |   15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 90ffc5f..5e5a605 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -5830,11 +5830,20 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, 
uint32_t count,
             *eax = cpu->phys_bits;
         }
         *ebx = env->features[FEAT_8000_0008_EBX];
-        *ecx = 0;
-        *edx = 0;
         if (cs->nr_cores * cs->nr_threads > 1) {
-            *ecx |= (cs->nr_cores * cs->nr_threads) - 1;
+            /*
+             * Bits 15:12 is "The number of bits in the initial
+             * Core::X86::Apic::ApicId[ApicId] value that indicate
+             * thread ID within a package". This is already stored at
+             * CPUX86State::pkg_offset.
+             * Bits 7:0 is "The number of threads in the package is NC+1"
+             */
+            *ecx = (env->pkg_offset << 12) |
+                   ((cs->nr_cores * cs->nr_threads) - 1);
+        } else {
+            *ecx = 0;
         }
+        *edx = 0;
         break;
     case 0x8000000A:
         if (env->features[FEAT_8000_0001_ECX] & CPUID_EXT3_SVM) {