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Date: Thu, 4 Apr 2024 14:30:28 -0700
From: Isaku Yamahata <isaku.yamahata@intel.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, michael.roth@amd.com,
	isaku.yamahata@intel.com, isaku.yamahata@linux.intel.com
Subject: Re: [PATCH v5 04/17] KVM: introduce new vendor op for
 KVM_GET_DEVICE_ATTR
Message-ID: <20240404213028.GQ2444378@ls.amr.corp.intel.com>
References: <20240404121327.3107131-1-pbonzini@redhat.com>
 <20240404121327.3107131-5-pbonzini@redhat.com>
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In-Reply-To: <20240404121327.3107131-5-pbonzini@redhat.com>

On Thu, Apr 04, 2024 at 08:13:14AM -0400,
Paolo Bonzini <pbonzini@redhat.com> 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.
> 
> Reviewed-by: Michael Roth <michael.roth@amd.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  arch/x86/include/asm/kvm-x86-ops.h |  1 +
>  arch/x86/include/asm/kvm_host.h    |  1 +
>  arch/x86/kvm/x86.c                 | 38 +++++++++++++++++++-----------
>  3 files changed, 26 insertions(+), 14 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm-x86-ops.h b/arch/x86/include/asm/kvm-x86-ops.h
> index 110d7f29ca9a..5187fcf4b610 100644
> --- a/arch/x86/include/asm/kvm-x86-ops.h
> +++ b/arch/x86/include/asm/kvm-x86-ops.h
> @@ -121,6 +121,7 @@ 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 16e07a2eee19..04c430eb25cf 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1778,6 +1778,7 @@ struct kvm_x86_ops {
>  	void (*enable_smi_window)(struct kvm_vcpu *vcpu);
>  #endif
>  
> +	int (*dev_get_attr)(u32 group, 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 3d2029402513..3934e7682734 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4842,34 +4842,44 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>  	return r;
>  }
>  
> -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 = u64_to_user_ptr(attr->addr);
> -
> -	if (attr->group)
> +	if (attr->group) {
> +		if (kvm_x86_ops.dev_get_attr)
> +			return static_call(kvm_x86_dev_get_attr)(attr->group, attr->attr, val);
>  		return -ENXIO;
> +	}
>  
>  	switch (attr->attr) {
>  	case KVM_X86_XCOMP_GUEST_SUPP:
> -		if (put_user(kvm_caps.supported_xcr0, uaddr))
> -			return -EFAULT;
> +		*val = kvm_caps.supported_xcr0;
>  		return 0;
>  	default:
>  		return -ENXIO;
>  	}
>  }
>  
> +static int kvm_x86_dev_get_attr(struct kvm_device_attr *attr)
> +{
> +	u64 __user *uaddr = u64_to_user_ptr(attr->addr);
> +	int r;
> +	u64 val;
> +
> +	r = __kvm_x86_dev_get_attr(attr, &val);
> +	if (r < 0)
> +		return r;
> +
> +	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,
> -- 
> 2.43.0
> 
> 
> 

Reviewed-by: Isaku Yamahata <isaku.yamahata@intel.com>
-- 
Isaku Yamahata <isaku.yamahata@intel.com>