Re: [PATCH v6 1/2] KVM: x86/cpuid: generalize kvm_update_kvm_cpuid_base() and also capture limit

[David Woodhouse]

On Tue, 2022-12-20 at 13:40 +0000, Paul Durrant wrote:
> A sunsequent patch will need to acquire the CPUID leaf range for emulated
> Xen so explicitly pass the signature of the hypervisor we're interested in
> to the new function. Also introduce a new kvm_hypervisor_cpuid structure
> so we can neatly store both the base and limit leaf indices.
> 
> Signed-off-by: Paul Durrant <pdurrant@xxxxxxxxxx>
> ---

Reviewed-by: David Woodhouse <dwmw@xxxxxxxxxxxx>

> Cc: Sean Christopherson <seanjc@xxxxxxxxxx>
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Cc: David Woodhouse <dwmw2@xxxxxxxxxxxxx>
> 
> v6:
>  - New in this version
> ---
>  arch/x86/include/asm/kvm_host.h |  7 ++++++-
>  arch/x86/kvm/cpuid.c            | 15 ++++++++-------
>  2 files changed, 14 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index f35f1ff4427b..ff201ad35551 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -710,6 +710,11 @@ struct kvm_queued_exception {
>         bool has_payload;
>  };
>  
> +struct kvm_hypervisor_cpuid {
> +       u32 base;
> +       u32 limit;
> +};
> +
>  struct kvm_vcpu_arch {
>         /*
>          * rip and regs accesses must go through
> @@ -826,7 +831,7 @@ struct kvm_vcpu_arch {
>  
>         int cpuid_nent;
>         struct kvm_cpuid_entry2 *cpuid_entries;
> -       u32 kvm_cpuid_base;
> +       struct kvm_hypervisor_cpuid kvm_cpuid;
>  
>         u64 reserved_gpa_bits;
>         int maxphyaddr;
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 0b5bf013fcb8..2468720f8d84 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -180,12 +180,13 @@ static int kvm_cpuid_check_equal(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2
>         return 0;
>  }
>  
> -static void kvm_update_kvm_cpuid_base(struct kvm_vcpu *vcpu)
> +static void kvm_update_hypervisor_cpuid(struct kvm_vcpu *vcpu, const char *hypervisor_signature,
> +                                       struct kvm_hypervisor_cpuid *hypervisor_cpuid)
>  {
>         u32 function;
>         struct kvm_cpuid_entry2 *entry;
>  
> -       vcpu->arch.kvm_cpuid_base = 0;
> +       memset(hypervisor_cpuid, 0, sizeof(*hypervisor_cpuid));
>  
>         for_each_possible_hypervisor_cpuid_base(function) {
>                 entry = kvm_find_cpuid_entry(vcpu, function);
> @@ -197,9 +198,9 @@ static void kvm_update_kvm_cpuid_base(struct kvm_vcpu *vcpu)
>                         signature[1] = entry->ecx;
>                         signature[2] = entry->edx;
>  
> -                       BUILD_BUG_ON(sizeof(signature) > sizeof(KVM_SIGNATURE));
> -                       if (!memcmp(signature, KVM_SIGNATURE, sizeof(signature))) {
> -                               vcpu->arch.kvm_cpuid_base = function;
> +                       if (!memcmp(signature, hypervisor_signature, sizeof(signature))) {
> +                               hypervisor_cpuid->base = function;
> +                               hypervisor_cpuid->limit = entry->eax;
>                                 break;
>                         }
>                 }
> @@ -209,7 +210,7 @@ static void kvm_update_kvm_cpuid_base(struct kvm_vcpu *vcpu)
>  static struct kvm_cpuid_entry2 *__kvm_find_kvm_cpuid_features(struct kvm_vcpu *vcpu,
>                                               struct kvm_cpuid_entry2 *entries, int nent)
>  {
> -       u32 base = vcpu->arch.kvm_cpuid_base;
> +       u32 base = vcpu->arch.kvm_cpuid.base;
>  
>         if (!base)
>                 return NULL;
> @@ -439,7 +440,7 @@ static int kvm_set_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2 *e2,
>         vcpu->arch.cpuid_entries = e2;
>         vcpu->arch.cpuid_nent = nent;
>  
> -       kvm_update_kvm_cpuid_base(vcpu);
> +       kvm_update_hypervisor_cpuid(vcpu, KVM_SIGNATURE, &vcpu->arch.kvm_cpuid);
>         kvm_vcpu_after_set_cpuid(vcpu);
>  
>         return 0;

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