[PATCH] target/i386: Avoid cpu number overflow in legacy topology

[Qian Wen <qian.wen@intel.com>]

The legacy topology enumerated by CPUID.1.EBX[23:16] is defined in SDM
Vol2:

Bits 23-16: Maximum number of addressable IDs for logical processors in
this physical package.

To avoid data overflow, limit the max value written to EBX[23:16] to
255.

Signed-off-by: Qian Wen <qian.wen@intel.com>
---
 target/i386/cpu.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 1294be374ab2..70589a58b727 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -5356,6 +5356,7 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
     uint32_t die_offset;
     uint32_t limit;
     uint32_t signature[3];
+    uint32_t threads_per_socket;
     X86CPUTopoInfo topo_info;
 
     topo_info.dies_per_pkg = env->nr_dies;
@@ -5397,8 +5398,18 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
             *ecx |= CPUID_EXT_OSXSAVE;
         }
         *edx = env->features[FEAT_1_EDX];
-        if (cs->nr_cores * cs->nr_threads > 1) {
-            *ebx |= (cs->nr_cores * cs->nr_threads) << 16;
+        /*
+         * The vCPU number more than 255 needs support of V2 Extended
+         * Topology enumerated by CPUID.0x1f or Extended Topology
+         * enumerated by CPUID.0x0b.
+         */
+        threads_per_socket = cs->nr_cores * cs->nr_threads;
+        if (threads_per_socket > 255) {
+            threads_per_socket = 255;
+        }
+
+        if (threads_per_socket > 1) {
+            *ebx |= threads_per_socket << 16;
             *edx |= CPUID_HT;
         }
         /*
-- 
2.25.1