Re: [PATCH 02/16] i386/cpu: Add descriptor 0x49 for CPUID 0x2 encoding

["Mi, Dapeng" <dapeng1.mi@linux.intel.com>]

On 6/20/2025 5:27 PM, Zhao Liu wrote:
> The legacy_l2_cache (2nd-level cache: 4 MByte, 16-way set associative,
> 64 byte line size) corresponds to descriptor 0x49, but at present
> cpuid2_cache_descriptors doesn't support descriptor 0x49 because it has
> multiple meanings.
>
> The 0x49 is necessary when CPUID 0x2 and 0x4 leaves have the consistent
> cache model, and use legacy_l2_cache as the default l2 cache.
>
> Therefore, add descriptor 0x49 to represent general l2 cache.
>
> Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
> ---
>  target/i386/cpu.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index e398868a3f8d..995766c9d74c 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -127,7 +127,18 @@ struct CPUID2CacheDescriptorInfo cpuid2_cache_descriptors[] = {
>                 .associativity = 8,  .line_size = 64, },
>      [0x48] = { .level = 2, .type = UNIFIED_CACHE,     .size =   3 * MiB,
>                 .associativity = 12, .line_size = 64, },
> -    /* Descriptor 0x49 depends on CPU family/model, so it is not included */
> +    /*
> +     * Descriptor 0x49 has 2 cases:
> +     *  - 2nd-level cache: 4 MByte, 16-way set associative, 64 byte line size.
> +     *  - 3rd-level cache: 4MB, 16-way set associative, 64-byte line size
> +     *    (Intel Xeon processor MP, Family 0FH, Model 06H).
> +     *
> +     * When it represents l3, then it depends on CPU family/model. Fortunately,
> +     * the legacy cache/CPU models don't have such special l3. So, just add it
> +     * to represent the general l2 case.

For comments and commit message, we'd better use the capital character
"L2/L3" to represent the 2nd/3rd level cache which is more conventional. 

Others look good to me.

Reviewed-by: Dapeng Mi <dapeng1.mi@linux.intel.com>


> +     */
> +    [0x49] = { .level = 2, .type = UNIFIED_CACHE,     .size =   4 * MiB,
> +               .associativity = 16, .line_size = 64, },
>      [0x4A] = { .level = 3, .type = UNIFIED_CACHE,     .size =   6 * MiB,
>                 .associativity = 12, .line_size = 64, },
>      [0x4B] = { .level = 3, .type = UNIFIED_CACHE,     .size =   8 * MiB,