linux-kernel - Re: [PATCH 02/10] KVM: introduce new vendor op for KVM_GET_DEVICE

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Date: Wed, 14 Feb 2024 16:57:49 -0600
From: Michael Roth <michael.roth@....com>
To: Paolo Bonzini <pbonzini@...hat.com>
CC: <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>,
	<seanjc@...gle.com>, <aik@....com>, <isaku.yamahata@...el.com>
Subject: Re: [PATCH 02/10] KVM: introduce new vendor op for
 KVM_GET_DEVICE_ATTR

On Fri, Feb 09, 2024 at 01:37:34PM -0500, Paolo Bonzini wrote:
> Allow vendor modules to provide their own attributes on /dev/kvm.
> To avoid proliferation of vendor ops, implement KVM_HAS_DEVICE_ATTR
> and KVM_GET_DEVICE_ATTR in terms of the same function.  You're not
> supposed to use KVM_GET_DEVICE_ATTR to do complicated computations,
> especially on /dev/kvm.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>

Reviewed-by: Michael Roth <michael.roth@....com>

> ---
>  arch/x86/include/asm/kvm-x86-ops.h |  1 +
>  arch/x86/include/asm/kvm_host.h    |  1 +
>  arch/x86/kvm/x86.c                 | 52 +++++++++++++++++++-----------
>  3 files changed, 36 insertions(+), 18 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm-x86-ops.h b/arch/x86/include/asm/kvm-x86-ops.h
> index 378ed944b849..ac8b7614e79d 100644
> --- a/arch/x86/include/asm/kvm-x86-ops.h
> +++ b/arch/x86/include/asm/kvm-x86-ops.h
> @@ -122,6 +122,7 @@ KVM_X86_OP(enter_smm)
>  KVM_X86_OP(leave_smm)
>  KVM_X86_OP(enable_smi_window)
>  #endif
> +KVM_X86_OP_OPTIONAL(dev_get_attr)
>  KVM_X86_OP_OPTIONAL(mem_enc_ioctl)
>  KVM_X86_OP_OPTIONAL(mem_enc_register_region)
>  KVM_X86_OP_OPTIONAL(mem_enc_unregister_region)
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index d271ba20a0b2..0bcd9ae16097 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1769,6 +1769,7 @@ struct kvm_x86_ops {
>  	void (*enable_smi_window)(struct kvm_vcpu *vcpu);
>  #endif
>  
> +	int (*dev_get_attr)(u64 attr, u64 *val);
>  	int (*mem_enc_ioctl)(struct kvm *kvm, void __user *argp);
>  	int (*mem_enc_register_region)(struct kvm *kvm, struct kvm_enc_region *argp);
>  	int (*mem_enc_unregister_region)(struct kvm *kvm, struct kvm_enc_region *argp);
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index bf10a9073a09..8746530930d5 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4804,37 +4804,53 @@ static inline void __user *kvm_get_attr_addr(struct kvm_device_attr *attr)
>  	return uaddr;
>  }
>  
> -static int kvm_x86_dev_get_attr(struct kvm_device_attr *attr)
> +static int __kvm_x86_dev_get_attr(struct kvm_device_attr *attr, u64 *val)
>  {
> -	u64 __user *uaddr = kvm_get_attr_addr(attr);
> +	int r;
>  
>  	if (attr->group)
>  		return -ENXIO;
>  
> +	switch (attr->attr) {
> +	case KVM_X86_XCOMP_GUEST_SUPP:
> +		r = 0;
> +		*val = kvm_caps.supported_xcr0;
> +		break;
> +	default:
> +		r = -ENXIO;
> +		if (kvm_x86_ops.dev_get_attr)
> +			r = kvm_x86_ops.dev_get_attr(attr->attr, val);
> +		break;
> +	}
> +
> +	return r;
> +}
> +
> +static int kvm_x86_dev_get_attr(struct kvm_device_attr *attr)
> +{
> +	u64 __user *uaddr;
> +	int r;
> +	u64 val;
> +
> +	r = __kvm_x86_dev_get_attr(attr, &val);
> +	if (r < 0)
> +		return r;
> +
> +	uaddr = kvm_get_attr_addr(attr);
>  	if (IS_ERR(uaddr))
>  		return PTR_ERR(uaddr);
>  
> -	switch (attr->attr) {
> -	case KVM_X86_XCOMP_GUEST_SUPP:
> -		if (put_user(kvm_caps.supported_xcr0, uaddr))
> -			return -EFAULT;
> -		return 0;
> -	default:
> -		return -ENXIO;
> -	}
> +	if (put_user(val, uaddr))
> +		return -EFAULT;
> +
> +	return 0;
>  }
>  
>  static int kvm_x86_dev_has_attr(struct kvm_device_attr *attr)
>  {
> -	if (attr->group)
> -		return -ENXIO;
> +	u64 val;
>  
> -	switch (attr->attr) {
> -	case KVM_X86_XCOMP_GUEST_SUPP:
> -		return 0;
> -	default:
> -		return -ENXIO;
> -	}
> +	return __kvm_x86_dev_get_attr(attr, &val);
>  }
>  
>  long kvm_arch_dev_ioctl(struct file *filp,
> -- 
> 2.39.0
> 
>