i386/cpu: Refine comment of CPUID2CacheDescriptorInfo

Refer to SDM vol.3 table 1-21, add the notes about the missing
descriptor, and fix the typo and comment format.

Reviewed-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Tested-by: Yi Lai <yi1.lai@intel.com>
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
Link: https://lore.kernel.org/r/20250711102143.1622339-2-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 f9e6bc8d0e6cf76b2c552179a2d99f2eb4b06c92..f107e5867348a0612e8bcd1c3f1ba6feb0493254 100644 (file)
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -68,6 +68,7 @@ struct CPUID2CacheDescriptorInfo {
 
 /*
  * Known CPUID 2 cache descriptors.
+ * TLB, prefetch and sectored cache related descriptors are not included.
  * From Intel SDM Volume 2A, CPUID instruction
  */
 struct CPUID2CacheDescriptorInfo cpuid2_cache_descriptors[] = {
@@ -89,18 +90,29 @@ struct CPUID2CacheDescriptorInfo cpuid2_cache_descriptors[] = {
                .associativity = 2,  .line_size = 64, },
     [0x21] = { .level = 2, .type = UNIFIED_CACHE,     .size = 256 * KiB,
                .associativity = 8,  .line_size = 64, },
-    /* lines per sector is not supported cpuid2_cache_descriptor(),
-    * so descriptors 0x22, 0x23 are not included
-    */
+    /*
+     * lines per sector is not supported cpuid2_cache_descriptor(),
+     * so descriptors 0x22, 0x23 are not included
+     */
     [0x24] = { .level = 2, .type = UNIFIED_CACHE,     .size =   1 * MiB,
                .associativity = 16, .line_size = 64, },
-    /* lines per sector is not supported cpuid2_cache_descriptor(),
-    * so descriptors 0x25, 0x20 are not included
-    */
+    /*
+     * lines per sector is not supported cpuid2_cache_descriptor(),
+     * so descriptors 0x25, 0x29 are not included
+     */
     [0x2C] = { .level = 1, .type = DATA_CACHE,        .size =  32 * KiB,
                .associativity = 8,  .line_size = 64, },
     [0x30] = { .level = 1, .type = INSTRUCTION_CACHE, .size =  32 * KiB,
                .associativity = 8,  .line_size = 64, },
+    /*
+     * Newer Intel CPUs (having the cores without L3, e.g., Intel MTL, ARL)
+     * use CPUID 0x4 leaf to describe cache topology, by encoding CPUID 0x2
+     * leaf with 0xFF. For older CPUs (without 0x4 leaf), it's also valid
+     * to just ignore L3's code if there's no L3.
+     *
+     * This already covers all the cases in QEMU, so code 0x40 is not
+     * included.
+     */
     [0x41] = { .level = 2, .type = UNIFIED_CACHE,     .size = 128 * KiB,
                .associativity = 4,  .line_size = 32, },
     [0x42] = { .level = 2, .type = UNIFIED_CACHE,     .size = 256 * KiB,
@@ -138,9 +150,10 @@ struct CPUID2CacheDescriptorInfo cpuid2_cache_descriptors[] = {
                .associativity = 4,  .line_size = 64, },
     [0x78] = { .level = 2, .type = UNIFIED_CACHE,     .size =   1 * MiB,
                .associativity = 4,  .line_size = 64, },
-    /* lines per sector is not supported cpuid2_cache_descriptor(),
-    * so descriptors 0x79, 0x7A, 0x7B, 0x7C are not included.
-    */
+    /*
+     * lines per sector is not supported cpuid2_cache_descriptor(),
+     * so descriptors 0x79, 0x7A, 0x7B, 0x7C are not included.
+     */
     [0x7D] = { .level = 2, .type = UNIFIED_CACHE,     .size =   2 * MiB,
                .associativity = 8,  .line_size = 64, },
     [0x7F] = { .level = 2, .type = UNIFIED_CACHE,     .size = 512 * KiB,