On 6/20/2025 5:27 PM, Zhao Liu wrote:
> As preparation for merging cache_info_cpuid4 and cache_info_amd in
> X86CPUState, set legacy cache model based on vendor in the CPUID 0x4
> leaf. For AMD CPU, select legacy AMD cache model (in cache_info_amd) as
> the default cache model, otherwise, select legacy Intel cache model (in
> cache_info_cpuid4) as before.
>
> To ensure compatibility is not broken, add an enable_legacy_vendor_cache
> flag based on x-vendor-only-v2 to indicate cases where the legacy cache
> model should be used regardless of the vendor. For CPUID 0x4 leaf,
> enable_legacy_vendor_cache flag indicates to pick legacy Intel cache
> model, which is for compatibility with the behavior of PC machine v10.0
> and older.
>
> The following explains how current vendor-based default legacy cache
> model ensures correctness without breaking compatibility.
>
> * For the PC machine v6.0 and older, vendor_cpuid_only=false, and
> vendor_cpuid_only_v2=false.
>
> - If the named CPU model has its own cache model, and doesn't use
> legacy cache model (legacy_cache=false), then cache_info_cpuid4 and
> cache_info_amd are same, so 0x4 leaf uses its own cache model
> regardless of the vendor.
>
> - For max/host/named CPU (without its own cache model), then the flag
> enable_legacy_vendor_cache is true, they will use legacy Intel cache
> model just like their previous behavior.
>
> * For the PC machine v10.0 and older (to v6.1), vendor_cpuid_only=true,
> and vendor_cpuid_only_v2=false.
>
> - If the named CPU model has its own cache model (legacy_cache=false),
> then cache_info_cpuid4 & cache_info_amd both equal to its own cache
> model, so it uses its own cache model in 0x4 leaf regardless of the
> vendor. Only AMD CPUs have all-0 leaf due to vendor_cpuid_only=true,
> and this is exactly the behavior of these old machines.
>
> - For max/host/named CPU (without its own cache model), then the flag
> enable_legacy_vendor_cache is true, they will use legacy Intel cache
> model. Similarly, only AMD CPUs have all-0 leaf, and this is exactly
> the behavior of these old machines.
>
> * For the PC machine v10.1 and newer, vendor_cpuid_only=true, and
> vendor_cpuid_only_v2=true.
>
> - If the named CPU model has its own cache model (legacy_cache=false),
> then cache_info_cpuid4 & cache_info_amd both equal to its own cache
> model, so it uses its own cache model in 0x4 leaf regardless of the
> vendor. And AMD CPUs have all-0 leaf. Nothing will change.
>
> - For max/host/named CPU (without its own cache model), then the flag
> enable_legacy_vendor_cache is false, the legacy cache model is
> selected based on vendor.
>
> For AMD CPU, it will use legacy AMD cache but still get all-0 leaf
> due to vendor_cpuid_only=true.
>
> For non-AMD (Intel/Zhaoxin) CPU, it will use legacy Intel cache as
> expected.
>
> Here, selecting the legacy cache model based on the vendor does not
> change the previous (before the change) behavior.
>
> Therefore, the above analysis proves that, with the help of the flag
> enable_legacy_vendor_cache, it is acceptable to select the default
> legacy cache model based on the vendor.
>
> For the CPUID 0x4 leaf, in X86CPUState, a unified cache_info is enough.
> It only needs to be initialized and configured with the corresponding
> legacy cache model based on the vendor.
>
> Signed-off-by: Zhao Liu <zhao1....@intel.com>
> ---
> target/i386/cpu.c | 43 ++++++++++++++++++++++++++++++++++---------
> 1 file changed, 34 insertions(+), 9 deletions(-)
>
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index 524d39de9ace..afbf11569ab4 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -7517,7 +7517,35 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index,
> uint32_t count,
> encode_cache_cpuid2(cpu, caches, eax, ebx, ecx, edx);
> break;
> }
> - case 4:
> + case 4: {
> + const CPUCaches *caches;
> +
> + if (env->enable_legacy_vendor_cache) {
> + caches = &legacy_intel_cache_info;
> + } else {
> + /*
> + * FIXME: Temporarily select cache info model here based on
> + * vendor, and merge these 2 cache info models later.
> + *
> + * This condition covers the following cases (with
> + * enable_legacy_vendor_cache=false):
> + * - When CPU model has its own cache model and doesn't use
> legacy
> + * cache model (legacy_model=off). Then cache_info_amd and
> + * cache_info_cpuid4 are the same.
> + *
> + * - For v10.1 and newer machines, when CPU model uses legacy
> cache
> + * model. Non-AMD CPUs use cache_info_cpuid4 like before and
> AMD
> + * CPU will use cache_info_amd. But this doesn't matter for
> AMD
> + * CPU, because this leaf encodes all-0 for AMD whatever its
> cache
> + * model is.
> + */
> + if (IS_AMD_CPU(env)) {
> + caches = &env->cache_info_amd;
> + } else {
> + caches = &env->cache_info_cpuid4;
> + }
> + }
> +
> /* cache info: needed for Core compatibility */
> if (cpu->cache_info_passthrough) {
> x86_cpu_get_cache_cpuid(index, count, eax, ebx, ecx, edx);
> @@ -7545,30 +7573,26 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index,
> uint32_t count,
>
> switch (count) {
> case 0: /* L1 dcache info */
> - encode_cache_cpuid4(env->cache_info_cpuid4.l1d_cache,
> - topo_info,
> + encode_cache_cpuid4(caches->l1d_cache, topo_info,
> eax, ebx, ecx, edx);
> if (!cpu->l1_cache_per_core) {
> *eax &= ~MAKE_64BIT_MASK(14, 12);
> }
> break;
> case 1: /* L1 icache info */
> - encode_cache_cpuid4(env->cache_info_cpuid4.l1i_cache,
> - topo_info,
> + encode_cache_cpuid4(caches->l1i_cache, topo_info,
> eax, ebx, ecx, edx);
> if (!cpu->l1_cache_per_core) {
> *eax &= ~MAKE_64BIT_MASK(14, 12);
> }
> break;
> case 2: /* L2 cache info */
> - encode_cache_cpuid4(env->cache_info_cpuid4.l2_cache,
> - topo_info,
> + encode_cache_cpuid4(caches->l2_cache, topo_info,
> eax, ebx, ecx, edx);
> break;
> case 3: /* L3 cache info */
> if (cpu->enable_l3_cache) {
> - encode_cache_cpuid4(env->cache_info_cpuid4.l3_cache,
> - topo_info,
> + encode_cache_cpuid4(caches->l3_cache, topo_info,
> eax, ebx, ecx, edx);
> break;
> }
> @@ -7579,6 +7603,7 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index,
> uint32_t count,
> }
> }
> break;
> + }
> case 5:
> /* MONITOR/MWAIT Leaf */
> *eax = cpu->mwait.eax; /* Smallest monitor-line size in bytes */
LGTM. Thanks.
Reviewed-by: Dapeng Mi <dapeng1...@linux.intel.com>
