linux-kernel - Re: [PATCH RESEND] KVM: X86: eliminate obsolete KVM_GET

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Message-ID: <87o8topadm.fsf@vitty.brq.redhat.com>
Date:   Mon, 24 Feb 2020 11:06:45 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     linmiaohe <linmiaohe@...wei.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org, x86@...nel.org,
        pbonzini@...hat.com, rkrcmar@...hat.com,
        sean.j.christopherson@...el.com, wanpengli@...cent.com,
        jmattson@...gle.com, joro@...tes.org, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, hpa@...or.com
Subject: Re: [PATCH RESEND] KVM: X86: eliminate obsolete KVM_GET_CPUID2 ioctl

linmiaohe <linmiaohe@...wei.com> writes:

> From: Miaohe Lin <linmiaohe@...wei.com>
>
> KVM_GET_CPUID2 ioctl is straight up broken 

It may make sense to add the gory details from your previous patch where
you were trying to fix it.

> and not used anywhere. Remove it directly.
>
> Suggested-by: Paolo Bonzini <pbonzini@...hat.com>
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
>  arch/x86/kvm/cpuid.c           | 20 --------------------
>  arch/x86/kvm/cpuid.h           |  3 ---
>  arch/x86/kvm/x86.c             | 17 -----------------
>  include/uapi/linux/kvm.h       |  1 -
>  tools/include/uapi/linux/kvm.h |  1 -
>  5 files changed, 42 deletions(-)
>
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index b1c469446b07..5e041a1282b8 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -261,26 +261,6 @@ int kvm_vcpu_ioctl_set_cpuid2(struct kvm_vcpu *vcpu,
>  	return r;
>  }
>  
> -int kvm_vcpu_ioctl_get_cpuid2(struct kvm_vcpu *vcpu,
> -			      struct kvm_cpuid2 *cpuid,
> -			      struct kvm_cpuid_entry2 __user *entries)
> -{
> -	int r;
> -
> -	r = -E2BIG;
> -	if (cpuid->nent < vcpu->arch.cpuid_nent)
> -		goto out;
> -	r = -EFAULT;
> -	if (copy_to_user(entries, &vcpu->arch.cpuid_entries,
> -			 vcpu->arch.cpuid_nent * sizeof(struct kvm_cpuid_entry2)))
> -		goto out;
> -	return 0;
> -
> -out:
> -	cpuid->nent = vcpu->arch.cpuid_nent;
> -	return r;
> -}
> -
>  static __always_inline void cpuid_mask(u32 *word, int wordnum)
>  {
>  	reverse_cpuid_check(wordnum);
> diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
> index 7366c618aa04..76555de38e1b 100644
> --- a/arch/x86/kvm/cpuid.h
> +++ b/arch/x86/kvm/cpuid.h
> @@ -19,9 +19,6 @@ int kvm_vcpu_ioctl_set_cpuid(struct kvm_vcpu *vcpu,
>  int kvm_vcpu_ioctl_set_cpuid2(struct kvm_vcpu *vcpu,
>  			      struct kvm_cpuid2 *cpuid,
>  			      struct kvm_cpuid_entry2 __user *entries);
> -int kvm_vcpu_ioctl_get_cpuid2(struct kvm_vcpu *vcpu,
> -			      struct kvm_cpuid2 *cpuid,
> -			      struct kvm_cpuid_entry2 __user *entries);
>  bool kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx,
>  	       u32 *ecx, u32 *edx, bool check_limit);
>  
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index fbabb2f06273..ddcc51b89e2c 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4286,23 +4286,6 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
>  					      cpuid_arg->entries);
>  		break;
>  	}
> -	case KVM_GET_CPUID2: {
> -		struct kvm_cpuid2 __user *cpuid_arg = argp;
> -		struct kvm_cpuid2 cpuid;
> -
> -		r = -EFAULT;
> -		if (copy_from_user(&cpuid, cpuid_arg, sizeof(cpuid)))
> -			goto out;
> -		r = kvm_vcpu_ioctl_get_cpuid2(vcpu, &cpuid,
> -					      cpuid_arg->entries);
> -		if (r)
> -			goto out;
> -		r = -EFAULT;
> -		if (copy_to_user(cpuid_arg, &cpuid, sizeof(cpuid)))
> -			goto out;
> -		r = 0;
> -		break;
> -	}
>  	case KVM_GET_MSRS: {
>  		int idx = srcu_read_lock(&vcpu->kvm->srcu);
>  		r = msr_io(vcpu, argp, do_get_msr, 1);
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 4b95f9a31a2f..b37b8c1f300e 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -1380,7 +1380,6 @@ struct kvm_s390_ucas_mapping {
>  #define KVM_GET_LAPIC             _IOR(KVMIO,  0x8e, struct kvm_lapic_state)
>  #define KVM_SET_LAPIC             _IOW(KVMIO,  0x8f, struct kvm_lapic_state)
>  #define KVM_SET_CPUID2            _IOW(KVMIO,  0x90, struct kvm_cpuid2)
> -#define KVM_GET_CPUID2            _IOWR(KVMIO, 0x91, struct kvm_cpuid2)

Even if we decide to be strong and remove KVM_GET_CPUID2 completely, I'd
suggest we leave a comment here saying that it was deprecated. Leaving
the branch in case (returning the same -EINVAL as passing an unsupported
IOCTL) may also make sense (with a 'deprecated' comment of course).

>  /* Available with KVM_CAP_VAPIC */
>  #define KVM_TPR_ACCESS_REPORTING  _IOWR(KVMIO, 0x92, struct kvm_tpr_access_ctl)
>  /* Available with KVM_CAP_VAPIC */
> diff --git a/tools/include/uapi/linux/kvm.h b/tools/include/uapi/linux/kvm.h
> index f0a16b4adbbd..431106dedd2c 100644
> --- a/tools/include/uapi/linux/kvm.h
> +++ b/tools/include/uapi/linux/kvm.h
> @@ -1379,7 +1379,6 @@ struct kvm_s390_ucas_mapping {
>  #define KVM_GET_LAPIC             _IOR(KVMIO,  0x8e, struct kvm_lapic_state)
>  #define KVM_SET_LAPIC             _IOW(KVMIO,  0x8f, struct kvm_lapic_state)
>  #define KVM_SET_CPUID2            _IOW(KVMIO,  0x90, struct kvm_cpuid2)
> -#define KVM_GET_CPUID2            _IOWR(KVMIO, 0x91, struct kvm_cpuid2)
>  /* Available with KVM_CAP_VAPIC */
>  #define KVM_TPR_ACCESS_REPORTING  _IOWR(KVMIO, 0x92, struct kvm_tpr_access_ctl)
>  /* Available with KVM_CAP_VAPIC */

-- 
Vitaly