linux-kernel - Re: [PATCH v2 1/7] KVM: X86: Reset vcpu->arch.cpuid_nent to 0 if SET

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Date:   Tue, 23 Jun 2020 11:20:31 -0700
From:   Jim Mattson <jmattson@...gle.com>
To:     Xiaoyao Li <xiaoyao.li@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>, kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/7] KVM: X86: Reset vcpu->arch.cpuid_nent to 0 if
 SET_CPUID fails

On Tue, Jun 23, 2020 at 4:58 AM Xiaoyao Li <xiaoyao.li@...el.com> wrote:
>
> It needs to invalidate CPUID configruations if usersapce provides

Nits: configurations, userspace

> illegal input.
>
> Signed-off-by: Xiaoyao Li <xiaoyao.li@...el.com>
> ---
>  arch/x86/kvm/cpuid.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 8a294f9747aa..1d13bad42bf9 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -207,6 +207,8 @@ int kvm_vcpu_ioctl_set_cpuid(struct kvm_vcpu *vcpu,
>         kvm_apic_set_version(vcpu);
>         kvm_x86_ops.cpuid_update(vcpu);
>         r = kvm_update_cpuid(vcpu);
> +       if (r)
> +               vcpu->arch.cpuid_nent = 0;
>
>         kvfree(cpuid_entries);
>  out:
> @@ -230,6 +232,8 @@ int kvm_vcpu_ioctl_set_cpuid2(struct kvm_vcpu *vcpu,
>         kvm_apic_set_version(vcpu);
>         kvm_x86_ops.cpuid_update(vcpu);
>         r = kvm_update_cpuid(vcpu);
> +       if (r)
> +               vcpu->arch.cpuid_nent = 0;
>  out:
>         return r;
>  }
> --
> 2.18.2

What if vcpu->arch.cpuid_nent was greater than 0 before the ioctl in question?