i386/cpu: Fix overflow of cache topology fields in CPUID.04H

According to SDM, CPUID.0x4:EAX[31:26] indicates the Maximum number of
addressable IDs for processor cores in the physical package. If we
launch over 64 cores VM, the 6-bit field will overflow, and the wrong
core_id number will be reported.

Since the HW reports 0x3f when the intel processor has over 64 cores,
limit the max value written to EAX[31:26] to 63, so max num_cores should
be 64.

For EAX[14:25], though at present Q35 supports up to 4096 CPUs, by
constructing a specific topology, the width of the APIC ID can be
extended beyond 12 bits. For example, using `-smp threads=33,cores=9,
modules=9` results in a die level offset of 6 + 4 + 4 = 14 bits, which
can also cause overflow.  check and honor the maximum value for
EAX[14:25] as well.

In addition, for host-cache-info case, also apply the same checks and
fixes.

Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Signed-off-by: Qian Wen <qian.wen@intel.com>
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
Link: https://lore.kernel.org/r/20250714080859.1960104-7-zhao1.liu@intel.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 608fdcf7578aed97958580863552e53ea4a947d1..fdc677614d8237fb77c6172f27b4cbc83dec7c34 100644 (file)
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -349,11 +349,17 @@ static void encode_cache_cpuid4(CPUCacheInfo *cache,
     assert(cache->size == cache->line_size * cache->associativity *
                           cache->partitions * cache->sets);
 
+    /*
+     * The following fields have bit-width limitations, so consider the
+     * maximum values to avoid overflow:
+     * Bits 25-14: maximum 4095.
+     * Bits 31-26: maximum 63.
+     */
     *eax = CACHE_TYPE(cache->type) |
            CACHE_LEVEL(cache->level) |
            (cache->self_init ? CACHE_SELF_INIT_LEVEL : 0) |
-           (max_core_ids_in_package(topo_info) << 26) |
-           (max_thread_ids_for_cache(topo_info, cache->share_level) << 14);
+           (MIN(max_core_ids_in_package(topo_info), 63) << 26) |
+           (MIN(max_thread_ids_for_cache(topo_info, cache->share_level), 4095) << 14);
 
     assert(cache->line_size > 0);
     assert(cache->partitions > 0);
@@ -7930,13 +7936,13 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
                 int host_vcpus_per_cache = 1 + ((*eax & 0x3FFC000) >> 14);
 
                 *eax &= ~0xFC000000;
-                *eax |= max_core_ids_in_package(topo_info) << 26;
+                *eax |= MIN(max_core_ids_in_package(topo_info), 63) << 26;
                 if (host_vcpus_per_cache > threads_per_pkg) {
                     *eax &= ~0x3FFC000;
 
                     /* Share the cache at package level. */
-                    *eax |= max_thread_ids_for_cache(topo_info,
-                                CPU_TOPOLOGY_LEVEL_SOCKET) << 14;
+                    *eax |= MIN(max_thread_ids_for_cache(topo_info,
+                                CPU_TOPOLOGY_LEVEL_SOCKET), 4095) << 14;
                 }
             }
         } else if (cpu->vendor_cpuid_only && IS_AMD_CPU(env)) {