Re: [PATCH v3 05/17] i386/cpu: Use APIC ID offset to encode cache topo in CPUID[4]

[Xiaoyao Li]

On 8/1/2023 6:35 PM, Zhao Liu wrote:
> From: Zhao Liu <zhao1.liu@intel.com>
>
> Refer to the fixes of cache_info_passthrough ([1], [2]) and SDM, the
> CPUID.04H:EAX[bits 25:14] and CPUID.04H:EAX[bits 31:26] should use the
> nearest power-of-2 integer.

I doubt it. Especially for [1].

SDM doesn't state it should be the nearest power-of-2 integer.
For example, regarding EAX[25:14], what SDM states are,

1. The value needs to be added with 1
　
2. The nearest power-of-2 integer that is not smaller than 
(1+EAX[25:14]) is the number of unique initial APIC IDs reserved for 
addressing different logical processor sharing this cache.

Above indicates that

1. "EAX[25:14] + 1", indicates the real number of how many LPs sharing 
this cache. i.e., how many APIC IDs

while 2. "The nearest power-of-2 integer that is not smaller than 
(EAX[25:14] + 1)" indicates the how many APIC IDs are reserved for LPs 
sharing this cache. It doesn't require EAX[25:14] + 1, to be power of 2.

> The nearest power-of-2 integer can be caculated by pow2ceil() or by
> using APIC ID offset (like L3 topology using 1 << die_offset [3]).
>
> But in fact, CPUID.04H:EAX[bits 25:14] and CPUID.04H:EAX[bits 31:26]
> are associated with APIC ID. For example, in linux kernel, the field
> "num_threads_sharing" (Bits 25 - 14) is parsed with APIC ID. And for
> another example, on Alder Lake P, the CPUID.04H:EAX[bits 31:26] is not
> matched with actual core numbers and it's caculated by:
> "(1 << (pkg_offset - core_offset)) - 1".
>
> Therefore the offset of APIC ID should be preferred to caculate nearest
> power-of-2 integer for CPUID.04H:EAX[bits 25:14] and CPUID.04H:EAX[bits
> 31:26]:
> 1. d/i cache is shared in a core, 1 << core_offset should be used
>     instand of "cs->nr_threads" in encode_cache_cpuid4() for
>     CPUID.04H.00H:EAX[bits 25:14] and CPUID.04H.01H:EAX[bits 25:14].
> 2. L2 cache is supposed to be shared in a core as for now, thereby
>     1 << core_offset should also be used instand of "cs->nr_threads" in
>     encode_cache_cpuid4() for CPUID.04H.02H:EAX[bits 25:14].
> 3. Similarly, the value for CPUID.04H:EAX[bits 31:26] should also be
>     replaced by the offsets upper SMT level in APIC ID.
>
> In addition, use APIC ID offset to replace "pow2ceil()" for
> cache_info_passthrough case.
>
> [1]: efb3934adf9e ("x86: cpu: make sure number of addressable IDs for processor 
> cores meets the spec")
> [2]: d7caf13b5fcf ("x86: cpu: fixup number of addressable IDs for logical processors 
> sharing cache")
> [3]: d65af288a84d ("i386: Update new x86_apicid parsing rules with die_offset 
> support")
>
> Fixes: 7e3482f82480 ("i386: Helpers to encode cache information consistently")
> Suggested-by: Robert Hoo <robert.hu@linux.intel.com>
> Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
> ---
> Changes since v1:
>   * Use APIC ID offset to replace "pow2ceil()" for cache_info_passthrough
>     case. (Yanan)
>   * Split the L1 cache fix into a separate patch.
>   * Rename the title of this patch (the original is "i386/cpu: Fix number
>     of addressable IDs in CPUID.04H").
> ---
>   target/i386/cpu.c | 30 +++++++++++++++++++++++-------
>   1 file changed, 23 insertions(+), 7 deletions(-)
>
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index b439a05244ee..c80613bfcded 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -6005,7 +6005,6 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, 
> uint32_t count,
>   {
>       X86CPU *cpu = env_archcpu(env);
>       CPUState *cs = env_cpu(env);
> -    uint32_t die_offset;
>       uint32_t limit;
>       uint32_t signature[3];
>       X86CPUTopoInfo topo_info;
> @@ -6089,39 +6088,56 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, 
> uint32_t count,
>                   int host_vcpus_per_cache = 1 + ((*eax & 0x3FFC000) >> 14);
>                   int vcpus_per_socket = cs->nr_cores * cs->nr_threads;
>                   if (cs->nr_cores > 1) {
> +                    int addressable_cores_offset =
> +                                                apicid_pkg_offset(&topo_info) -
> +                                                apicid_core_offset(&topo_info);
> +
>                       *eax &= ~0xFC000000;
> -                    *eax |= (pow2ceil(cs->nr_cores) - 1) << 26;
> +                    *eax |= (1 << addressable_cores_offset - 1) << 26;
>                   }
>                   if (host_vcpus_per_cache > vcpus_per_socket) {
> +                    int pkg_offset = apicid_pkg_offset(&topo_info);
> +
>                       *eax &= ~0x3FFC000;
> -                    *eax |= (pow2ceil(vcpus_per_socket) - 1) << 14;
> +                    *eax |= (1 << pkg_offset - 1) << 14;
>                   }
>               }
>           } else if (cpu->vendor_cpuid_only && IS_AMD_CPU(env)) {
>               *eax = *ebx = *ecx = *edx = 0;
>           } else {
>               *eax = 0;
> +            int addressable_cores_offset = apicid_pkg_offset(&topo_info) -
> +                                           apicid_core_offset(&topo_info);
> +            int core_offset, die_offset;
> +
>               switch (count) {
>               case 0: /* L1 dcache info */
> +                core_offset = apicid_core_offset(&topo_info);
>                   encode_cache_cpuid4(env->cache_info_cpuid4.l1d_cache,
> -                                    cs->nr_threads, cs->nr_cores,
> +                                    (1 << core_offset),
> +                                    (1 << addressable_cores_offset),
>                                       eax, ebx, ecx, edx);
>                   break;
>               case 1: /* L1 icache info */
> +                core_offset = apicid_core_offset(&topo_info);
>                   encode_cache_cpuid4(env->cache_info_cpuid4.l1i_cache,
> -                                    cs->nr_threads, cs->nr_cores,
> +                                    (1 << core_offset),
> +                                    (1 << addressable_cores_offset),
>                                       eax, ebx, ecx, edx);
>                   break;
>               case 2: /* L2 cache info */
> +                core_offset = apicid_core_offset(&topo_info);
>                   encode_cache_cpuid4(env->cache_info_cpuid4.l2_cache,
> -                                    cs->nr_threads, cs->nr_cores,
> +                                    (1 << core_offset),
> +                                    (1 << addressable_cores_offset),
>                                       eax, ebx, ecx, edx);
>                   break;
>               case 3: /* L3 cache info */
>                   die_offset = apicid_die_offset(&topo_info);
>                   if (cpu->enable_l3_cache) {
>                       encode_cache_cpuid4(env->cache_info_cpuid4.l3_cache,
> -                                        (1 << die_offset), cs->nr_cores,
> +                                        (1 << die_offset),
> +                                        (1 << addressable_cores_offset),
>                                           eax, ebx, ecx, edx);
>                       break;
>                   }