linux-kernel - Re: [Patch v4 02/13] KVM: x86: Add a KVM-only leaf for CPUID_8000_0007

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Date:   Tue, 27 Dec 2022 20:20:08 +0000
From:   Aaron Lewis <aaronlewis@...gle.com>
To:     Vipin Sharma <vipinsh@...gle.com>
Cc:     seanjc@...gle.com, pbonzini@...hat.com, vkuznets@...hat.com,
        dmatlack@...gle.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [Patch v4 02/13] KVM: x86: Add a KVM-only leaf for CPUID_8000_0007_EDX

On Mon, Dec 12, 2022 at 6:37 PM Vipin Sharma <vipinsh@...gle.com> wrote:
>
> From: Vitaly Kuznetsov <vkuznets@...hat.com>
>
> CPUID_8000_0007_EDX may come handy when X86_FEATURE_CONSTANT_TSC
> needs to be checked.
>
> No functional change intended.
>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> Reviewed-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/cpuid.c         | 8 ++++++--
>  arch/x86/kvm/reverse_cpuid.h | 7 +++++++
>  2 files changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 723502181a3a..42913695fedd 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -701,6 +701,10 @@ void kvm_set_cpu_caps(void)
>         if (!tdp_enabled && IS_ENABLED(CONFIG_X86_64))
>                 kvm_cpu_cap_set(X86_FEATURE_GBPAGES);
>
> +       kvm_cpu_cap_init_kvm_defined(CPUID_8000_0007_EDX,
> +               SF(CONSTANT_TSC)
> +       );
> +
>         kvm_cpu_cap_mask(CPUID_8000_0008_EBX,
>                 F(CLZERO) | F(XSAVEERPTR) |
>                 F(WBNOINVD) | F(AMD_IBPB) | F(AMD_IBRS) | F(AMD_SSBD) | F(VIRT_SSBD) |
> @@ -1153,8 +1157,8 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
>                 entry->edx &= ~GENMASK(17, 16);
>                 break;
>         case 0x80000007: /* Advanced power management */
> -               /* invariant TSC is CPUID.80000007H:EDX[8] */
> -               entry->edx &= (1 << 8);
> +               cpuid_entry_override(entry, CPUID_8000_0007_EDX);
> +
>                 /* mask against host */
>                 entry->edx &= boot_cpu_data.x86_power;
>                 entry->eax = entry->ebx = entry->ecx = 0;
> diff --git a/arch/x86/kvm/reverse_cpuid.h b/arch/x86/kvm/reverse_cpuid.h
> index 203fdad07bae..25b9b51abb20 100644
> --- a/arch/x86/kvm/reverse_cpuid.h
> +++ b/arch/x86/kvm/reverse_cpuid.h
> @@ -14,6 +14,7 @@
>  enum kvm_only_cpuid_leafs {
>         CPUID_12_EAX     = NCAPINTS,
>         CPUID_7_1_EDX,
> +       CPUID_8000_0007_EDX,
>         NR_KVM_CPU_CAPS,
>
>         NKVMCAPINTS = NR_KVM_CPU_CAPS - NCAPINTS,
> @@ -42,6 +43,9 @@ enum kvm_only_cpuid_leafs {
>  #define X86_FEATURE_AVX_NE_CONVERT      KVM_X86_FEATURE(CPUID_7_1_EDX, 5)
>  #define X86_FEATURE_PREFETCHITI         KVM_X86_FEATURE(CPUID_7_1_EDX, 14)
>
> +/* CPUID level 0x80000007 (EDX). */
> +#define KVM_X86_FEATURE_CONSTANT_TSC   KVM_X86_FEATURE(CPUID_8000_0007_EDX, 8)
> +
>  struct cpuid_reg {
>         u32 function;
>         u32 index;
> @@ -67,6 +71,7 @@ static const struct cpuid_reg reverse_cpuid[] = {
>         [CPUID_12_EAX]        = {0x00000012, 0, CPUID_EAX},
>         [CPUID_8000_001F_EAX] = {0x8000001f, 0, CPUID_EAX},
>         [CPUID_7_1_EDX]       = {         7, 1, CPUID_EDX},
> +       [CPUID_8000_0007_EDX] = {0x80000007, 0, CPUID_EDX},
>  };
>
>  /*
> @@ -97,6 +102,8 @@ static __always_inline u32 __feature_translate(int x86_feature)
>                 return KVM_X86_FEATURE_SGX1;
>         else if (x86_feature == X86_FEATURE_SGX2)
>                 return KVM_X86_FEATURE_SGX2;
> +       else if (x86_feature == X86_FEATURE_CONSTANT_TSC)
> +               return KVM_X86_FEATURE_CONSTANT_TSC;
>
>         return x86_feature;
>  }
> --
> 2.39.0.rc1.256.g54fd8350bd-goog
>

I believe this version of the patch should have been taken instead of:
https://git.kernel.org/pub/scm/virt/kvm/kvm.git/commit/?h=queue&id=42b76c1ae40b89716c7a804cb575a4b52eb4e12f

I think it should be kvm_cpu_cap_init_kvm_defined() rather than
kvm_cpu_cap_init_scattered().

I'm getting this:
arch/x86/kvm/cpuid.c:705:2: error: call to undeclared function
'kvm_cpu_cap_init_scattered'; ISO C99 and later do not support
implicit function declarations [-Wimplicit-function-declaration]
        kvm_cpu_cap_init_scattered(CPUID_8000_0007_EDX,
        ^
arch/x86/kvm/cpuid.c:705:2: note: did you mean 'kvm_cpu_cap_init_kvm_defined'?
arch/x86/kvm/cpuid.c:553:6: note: 'kvm_cpu_cap_init_kvm_defined' declared here
void kvm_cpu_cap_init_kvm_defined(enum kvm_only_cpuid_leafs leaf, u32 mask)
     ^
1 error generated.