[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>
---
 target/i386/cpu.c |   12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 90ffc5f..68210f6 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -5830,11 +5830,17 @@ 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;
+            unsigned int max_apicids, bits_required;
+
+            max_apicids = (cs->nr_cores * cs->nr_threads) - 1;
+            /* Find out the number of bits to represent all the apicids */
+            bits_required = 32 - clz32(max_apicids);
+            *ecx = bits_required << 12 | max_apicids;
+        } else {
+            *ecx = 0;
         }
+        *edx = 0;
         break;
     case 0x8000000A:
         if (env->features[FEAT_8000_0001_ECX] & CPUID_EXT3_SVM) {