Re: [PATCH] target/i386: Fix reporting of CPU dies when nr_cores=nr_threads=1

[Wen, Qian]

On 7/24/2023 2:59 AM, 小太 wrote:
> When QEMU is started with `-smp D,sockets=1,dies=D,cores=1,threads=1` (that
> is, 1 socket with D dies but each die contains just a single thread), both
> Linux and Windows guests incorrectly interprets the system as having D
> sockets with 1 die each
> 
> Ultimately this is caused by various CPUID leaves not being die-aware in
> their "threads per socket" calculations, so this patch fixes that
> 
> These changes are referenced to the AMD PPR for Family 19h Model 01h (Milan)
> and Family 17h Model 01h (Naples) manuals:
>  - CPUID_Fn00000001_EBX[23:16]: Number of threads in the processor
>                                 (Core::X86::Cpuid::SizeId[NC] + 1)
>  - CPUID_Fn0000000B_EBX_x01[15:0]: Number of logical cores in processor
>                                    socket (not present until Rome)
>  - CPUID_Fn80000001_ECX[1]: Multi core product
>                             (Core::X86::Cpuid::SizeId[NC] != 0)
>  - CPUID_Fn80000008_ECX[7:0]: The number of threads in the package - 1
>                               (Core::X86::Cpuid::SizeId[NC])
> 
> Note there are two remaining occurences that I didn't touch:
>  - CPUID_Fn8000001E_ECX[10:8]: Always 0 (1 node per processor) for Milan.
>                                But for Naples, it can also be 2 or 4 nodes
>                                where each node is defined as one or two
>                                CCXes (CCD?). But Milan also has multiple
>                                CCXes, so clearly the definition of a node is
>                                different from model to model, so I've left
>                                it untouched. (QEMU seems to use the Naples
>                                definition)
>  - MSR_CORE_THREAD_COUNT: This MSR doesn't exist on Milan or Naples
> 
> Signed-off-by: 小太 <nospam@kota.moe>
> ---
>  target/i386/cpu.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index 97ad229d8b..6ff23fa590 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -6049,8 +6049,8 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, 
> uint32_t count,
>              *ecx |= CPUID_EXT_OSXSAVE;
>          }
>          *edx = env->features[FEAT_1_EDX];
> -        if (cs->nr_cores * cs->nr_threads > 1) {
> -            *ebx |= (cs->nr_cores * cs->nr_threads) << 16;
> +        if (env->nr_dies * cs->nr_cores * cs->nr_threads > 1) {
> +            *ebx |= (env->nr_dies * cs->nr_cores * cs->nr_threads) << 16;

The nr_cores in CPUState means "Number of cores within this CPU package", so it 
doesn't need
"nr_dies" here. Zhao Liu is fixing the calculation of nr_cores [1].

[1]: https://lists.gnu.org/archive/html/qemu-devel/2023-05/msg07187.html

Thanks,
Qian

>              *edx |= CPUID_HT;
>          }
>          if (!cpu->enable_pmu) {
> @@ -6230,7 +6230,7 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, 
> uint32_t count,
>              break;
>          case 1:
>              *eax = apicid_pkg_offset(&topo_info);
> -            *ebx = cs->nr_cores * cs->nr_threads;
> +            *ebx = env->nr_dies * cs->nr_cores * cs->nr_threads;
>              *ecx |= CPUID_TOPOLOGY_LEVEL_CORE;
>              break;
>          default:
> @@ -6496,7 +6496,7 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, 
> uint32_t count,
>           * discards multiple thread information if it is set.
>           * So don't set it here for Intel to make Linux guests happy.
>           */
> -        if (cs->nr_cores * cs->nr_threads > 1) {
> +        if (env->nr_dies * cs->nr_cores * cs->nr_threads > 1) {
>              if (env->cpuid_vendor1 != CPUID_VENDOR_INTEL_1 ||
>                  env->cpuid_vendor2 != CPUID_VENDOR_INTEL_2 ||
>                  env->cpuid_vendor3 != CPUID_VENDOR_INTEL_3) {
> @@ -6562,7 +6562,7 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, 
> uint32_t count,
>               *eax |= (cpu_x86_virtual_addr_width(env) << 8);
>          }
>          *ebx = env->features[FEAT_8000_0008_EBX];
> -        if (cs->nr_cores * cs->nr_threads > 1) {
> +        if (env->nr_dies * cs->nr_cores * cs->nr_threads > 1) {
>              /*
>               * Bits 15:12 is "The number of bits in the initial
>               * Core::X86::Apic::ApicId[ApicId] value that indicate
> @@ -6570,7 +6570,7 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, 
> uint32_t count,
>               * Bits 7:0 is "The number of threads in the package is NC+1"
>               */
>              *ecx = (apicid_pkg_offset(&topo_info) << 12) |
> -                   ((cs->nr_cores * cs->nr_threads) - 1);
> +                   ((env->nr_dies * cs->nr_cores * cs->nr_threads) - 1);
>          } else {
>              *ecx = 0;
>          }