Re: [PATCH v2] i386/cpu: Introduce enable_cpuid_0x1f to force exposing CPUID 0x1f

[Igor Mammedov <imammedo@redhat.com>]

On Mon, 12 Aug 2024 23:31:45 -0400
Xiaoyao Li <xiaoyao.li@intel.com> wrote:

> Currently, QEMU exposes CPUID 0x1f to guest only when necessary, i.e.,
> when topology level that cannot be enumerated by leaf 0xB, e.g., die or
> module level, are configured for the guest, e.g., -smp xx,dies=2.
> 
> However, 1) TDX architecture forces to require CPUID 0x1f to configure CPU
> topology. and 2) There is a bug in Windows that Windows 10/11 expects valid
> 0x1f leafs when the maximum basic leaf > 0x1f[1].
 1. will it boot if you use older cpu model?
 2. how user would know that this option would be needed?

> 
> Introduce a bool flag, enable_cpuid_0x1f, in CPU for the cases that
> require CPUID leaf 0x1f to be exposed to guest. For case 2), introduce
> a user settable property, "x-cpuid-0x1f" ,as well, which provides an opt-in
> interface for people to run the buggy Windows as a workaround. The default
> value of the property is set to false, thus making no effect on existing
> setup.
> 
> Introduce a new function x86_has_cpuid_0x1f(), which is the warpper of
> cpu->enable_cpuid_0x1f and x86_has_extended_topo() to check if it needs
> to enable cpuid leaf 0x1f for the guest.
> 
> [1] https://lore.kernel.org/qemu-devel/20240724075226.212882-1-manish.mishra@nutanix.com/
> 
> Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
> ---
> changes in v2:
>  - Add more details in commit message;
>  - introduce a separate function x86_has_cpuid_0x1f() instead of
>    modifying x86_has_extended_topo();
> ---
>  target/i386/cpu.c     | 5 +++--
>  target/i386/cpu.h     | 9 +++++++++
>  target/i386/kvm/kvm.c | 2 +-
>  3 files changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index 85ef7452c04e..1e8653c6b051 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -6649,7 +6649,7 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
>          break;
>      case 0x1F:
>          /* V2 Extended Topology Enumeration Leaf */
> -        if (!x86_has_extended_topo(env->avail_cpu_topo)) {
> +        if (!x86_has_cpuid_0x1f(cpu)) {
>              *eax = *ebx = *ecx = *edx = 0;
>              break;
>          }
> @@ -7462,7 +7462,7 @@ void x86_cpu_expand_features(X86CPU *cpu, Error **errp)
>           * cpu->vendor_cpuid_only has been unset for compatibility with older
>           * machine types.
>           */
> -        if (x86_has_extended_topo(env->avail_cpu_topo) &&
> +        if (x86_has_cpuid_0x1f(cpu) &&
>              (IS_INTEL_CPU(env) || !cpu->vendor_cpuid_only)) {
>              x86_cpu_adjust_level(cpu, &env->cpuid_min_level, 0x1F);
>          }
> @@ -8328,6 +8328,7 @@ static Property x86_cpu_properties[] = {
>      DEFINE_PROP_BOOL("full-cpuid-auto-level", X86CPU, full_cpuid_auto_level, true),
>      DEFINE_PROP_STRING("hv-vendor-id", X86CPU, hyperv_vendor),
>      DEFINE_PROP_BOOL("cpuid-0xb", X86CPU, enable_cpuid_0xb, true),
> +    DEFINE_PROP_BOOL("x-cpuid-0x1f", X86CPU, enable_cpuid_0x1f, false),
>      DEFINE_PROP_BOOL("x-vendor-cpuid-only", X86CPU, vendor_cpuid_only, true),
>      DEFINE_PROP_BOOL("x-amd-topoext-features-only", X86CPU, amd_topoext_features_only, true),
>      DEFINE_PROP_BOOL("lmce", X86CPU, enable_lmce, false),
> diff --git a/target/i386/cpu.h b/target/i386/cpu.h
> index c6cc035df3d8..085272d4c74a 100644
> --- a/target/i386/cpu.h
> +++ b/target/i386/cpu.h
> @@ -2110,6 +2110,9 @@ struct ArchCPU {
>      /* Compatibility bits for old machine types: */
>      bool enable_cpuid_0xb;
>  
> +    /* Force to enable cpuid 0x1f */
> +    bool enable_cpuid_0x1f;
> +
>      /* Enable auto level-increase for all CPUID leaves */
>      bool full_cpuid_auto_level;
>  
> @@ -2369,6 +2372,12 @@ void host_cpuid(uint32_t function, uint32_t count,
>                  uint32_t *eax, uint32_t *ebx, uint32_t *ecx, uint32_t *edx);
>  bool cpu_has_x2apic_feature(CPUX86State *env);
>  
> +static inline bool x86_has_cpuid_0x1f(X86CPU *cpu)
> +{
> +    return cpu->enable_cpuid_0x1f ||
> +           x86_has_extended_topo(cpu->env.avail_cpu_topo);
> +}
> +
>  /* helper.c */
>  void x86_cpu_set_a20(X86CPU *cpu, int a20_state);
>  void cpu_sync_avx_hflag(CPUX86State *env);
> diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
> index 31f149c9902c..8af43cb48101 100644
> --- a/target/i386/kvm/kvm.c
> +++ b/target/i386/kvm/kvm.c
> @@ -1835,7 +1835,7 @@ static uint32_t kvm_x86_build_cpuid(CPUX86State *env,
>              break;
>          }
>          case 0x1f:
> -            if (!x86_has_extended_topo(env->avail_cpu_topo)) {
> +            if (!x86_has_cpuid_0x1f(env_archcpu(env))) {
>                  cpuid_i--;
>                  break;
>              }