Re: [PATCH v7 08/16] i386: Expose module level in CPUID[0x1F]

[Zhao Liu <zhao1.liu@linux.intel.com>]

Hi Yuan,

On Mon, Jan 15, 2024 at 11:25:24AM +0800, Yuan Yao wrote:
> Date: Mon, 15 Jan 2024 11:25:24 +0800
> From: Yuan Yao <yuan.yao@linux.intel.com>
> Subject: Re: [PATCH v7 08/16] i386: Expose module level in CPUID[0x1F]
> 
> On Mon, Jan 08, 2024 at 04:27:19PM +0800, Zhao Liu wrote:
> > From: Zhao Liu <zhao1.liu@intel.com>
> >
> > Linux kernel (from v6.4, with commit edc0a2b595765 ("x86/topology: Fix
> > erroneous smp_num_siblings on Intel Hybrid platforms") is able to
> > handle platforms with Module level enumerated via CPUID.1F.
> >
> > Expose the module level in CPUID[0x1F] if the machine has more than 1
> > modules.
> >
> > (Tested CPU topology in CPUID[0x1F] leaf with various die/cluster
> > configurations in "-smp".)
> >
> > Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
> > Tested-by: Babu Moger <babu.moger@amd.com>
> > Tested-by: Yongwei Ma <yongwei.ma@intel.com>
> > Acked-by: Michael S. Tsirkin <mst@redhat.com>
> > ---
> > Changes since v3:
> >  * New patch to expose module level in 0x1F.
> >  * Add Tested-by tag from Yongwei.
> > ---
> >  target/i386/cpu.c     | 12 +++++++++++-
> >  target/i386/cpu.h     |  2 ++
> >  target/i386/kvm/kvm.c |  2 +-
> >  3 files changed, 14 insertions(+), 2 deletions(-)
> >
> > diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> > index 294ca6b8947a..a2d39d2198b6 100644
> > --- a/target/i386/cpu.c
> > +++ b/target/i386/cpu.c
> > @@ -277,6 +277,8 @@ static uint32_t num_cpus_by_topo_level(X86CPUTopoInfo *topo_info,
> >          return 1;
> >      case CPU_TOPO_LEVEL_CORE:
> >          return topo_info->threads_per_core;
> > +    case CPU_TOPO_LEVEL_MODULE:
> > +        return topo_info->threads_per_core * topo_info->cores_per_module;
> >      case CPU_TOPO_LEVEL_DIE:
> >          return topo_info->threads_per_core * topo_info->cores_per_module *
> >                 topo_info->modules_per_die;
> > @@ -297,6 +299,8 @@ static uint32_t apicid_offset_by_topo_level(X86CPUTopoInfo *topo_info,
> >          return 0;
> >      case CPU_TOPO_LEVEL_CORE:
> >          return apicid_core_offset(topo_info);
> > +    case CPU_TOPO_LEVEL_MODULE:
> > +        return apicid_module_offset(topo_info);
> >      case CPU_TOPO_LEVEL_DIE:
> >          return apicid_die_offset(topo_info);
> >      case CPU_TOPO_LEVEL_PACKAGE:
> > @@ -316,6 +320,8 @@ static uint32_t cpuid1f_topo_type(enum CPUTopoLevel topo_level)
> >          return CPUID_1F_ECX_TOPO_LEVEL_SMT;
> >      case CPU_TOPO_LEVEL_CORE:
> >          return CPUID_1F_ECX_TOPO_LEVEL_CORE;
> > +    case CPU_TOPO_LEVEL_MODULE:
> > +        return CPUID_1F_ECX_TOPO_LEVEL_MODULE;
> >      case CPU_TOPO_LEVEL_DIE:
> >          return CPUID_1F_ECX_TOPO_LEVEL_DIE;
> >      default:
> > @@ -347,6 +353,10 @@ static void encode_topo_cpuid1f(CPUX86State *env, uint32_t count,
> >          if (env->nr_dies > 1) {
> >              set_bit(CPU_TOPO_LEVEL_DIE, topo_bitmap);
> >          }
> > +
> > +        if (env->nr_modules > 1) {
> > +            set_bit(CPU_TOPO_LEVEL_MODULE, topo_bitmap);
> > +        }
> >      }
> >
> >      *ecx = count & 0xff;
> > @@ -6394,7 +6404,7 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
> >          break;
> >      case 0x1F:
> >          /* V2 Extended Topology Enumeration Leaf */
> > -        if (topo_info.dies_per_pkg < 2) {
> > +        if (topo_info.modules_per_die < 2 && topo_info.dies_per_pkg < 2) {
> 
> A question:
> Is the original checking necessary ?
> The 0x1f exists even on cpu w/o modules/dies topology on bare metal, I tried
> on EMR:
> 
> // leaf 0
> 0x00000000 0x00: eax=0x00000020 ebx=0x756e6547 ecx=0x6c65746e edx=0x49656e69
> 
> // leaf 0x1f
> 0x0000001f 0x00: eax=0x00000001 ebx=0x00000002 ecx=0x00000100 edx=0x00000004
> 0x0000001f 0x01: eax=0x00000007 ebx=0x00000080 ecx=0x00000201 edx=0x00000004
> 0x0000001f 0x02: eax=0x00000000 ebx=0x00000000 ecx=0x00000002 edx=0x00000004
> 
> // leaf 0xb
> 0x0000000b 0x00: eax=0x00000001 ebx=0x00000002 ecx=0x00000100 edx=0x00000004
> 0x0000000b 0x01: eax=0x00000007 ebx=0x00000080 ecx=0x00000201 edx=0x00000004
> 0x0000000b 0x02: eax=0x00000000 ebx=0x00000000 ecx=0x00000002 edx=0x00000004

The 0x1f is introduced for CascadeLake-AP with die level. And yes the
newer mahcines all have this leaf.

> 
> So here leads to different cpu behavior from bare metal, even in case
> of "-cpu host".
> 
> In SDM Vol2, cpudid instruction section:
> 
> " CPUID leaf 1FH is a preferred superset to leaf 0BH. Intel
> recommends using leaf 1FH when available rather than leaf
> 0BH and ensuring that any leaf 0BH algorithms are updated to
> support leaf 1FH. "
> 
> My understanding: if 0x1f is existed (leaf 0.eax >= 0x1f)
> then it should have same values in lp/core level as 0xb.

Yes, I think it's time to move to default 0x1f.

The compatibility issue can be solved by a cpuid-0x1f option similar to
cpuid-0xb. I'll cook a patch after this patch series.

Thanks,
Zhao

> 
> >              *eax = *ebx = *ecx = *edx = 0;
> >              break;
> >          }
> > diff --git a/target/i386/cpu.h b/target/i386/cpu.h
> > index eecd30bde92b..97b290e10576 100644
> > --- a/target/i386/cpu.h
> > +++ b/target/i386/cpu.h
> > @@ -1018,6 +1018,7 @@ enum CPUTopoLevel {
> >      CPU_TOPO_LEVEL_INVALID,
> >      CPU_TOPO_LEVEL_SMT,
> >      CPU_TOPO_LEVEL_CORE,
> > +    CPU_TOPO_LEVEL_MODULE,
> >      CPU_TOPO_LEVEL_DIE,
> >      CPU_TOPO_LEVEL_PACKAGE,
> >      CPU_TOPO_LEVEL_MAX,
> > @@ -1032,6 +1033,7 @@ enum CPUTopoLevel {
> >  #define CPUID_1F_ECX_TOPO_LEVEL_INVALID  CPUID_B_ECX_TOPO_LEVEL_INVALID
> >  #define CPUID_1F_ECX_TOPO_LEVEL_SMT      CPUID_B_ECX_TOPO_LEVEL_SMT
> >  #define CPUID_1F_ECX_TOPO_LEVEL_CORE     CPUID_B_ECX_TOPO_LEVEL_CORE
> > +#define CPUID_1F_ECX_TOPO_LEVEL_MODULE   3
> >  #define CPUID_1F_ECX_TOPO_LEVEL_DIE      5
> >
> >  /* MSR Feature Bits */
> > diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
> > index 4ce80555b45c..e5ddb214cb36 100644
> > --- a/target/i386/kvm/kvm.c
> > +++ b/target/i386/kvm/kvm.c
> > @@ -1913,7 +1913,7 @@ int kvm_arch_init_vcpu(CPUState *cs)
> >              break;
> >          }
> >          case 0x1f:
> > -            if (env->nr_dies < 2) {
> > +            if (env->nr_modules < 2 && env->nr_dies < 2) {
> >                  break;
> >              }
> >              /* fallthrough */
> > --
> > 2.34.1
> >
> >