linux-kernel - Re: [PATCH 2/3 v2] KVM: nVMX: Enable VMFUNC for the L1 hypervisor

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Date:   Mon, 10 Jul 2017 11:17:50 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Bandan Das <bsd@...hat.com>, kvm@...r.kernel.org
Cc:     pbonzini@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3 v2] KVM: nVMX: Enable VMFUNC for the L1 hypervisor


> @@ -7752,7 +7769,29 @@ static int handle_preemption_timer(struct kvm_vcpu *vcpu)
>  
>  static int handle_vmfunc(struct kvm_vcpu *vcpu)
>  {
> -	kvm_queue_exception(vcpu, UD_VECTOR);
> +	struct vcpu_vmx *vmx = to_vmx(vcpu);
> +	struct vmcs12 *vmcs12;
> +	u32 function = vcpu->arch.regs[VCPU_REGS_RAX];
> +
> +	/*
> +	 * VMFUNC is only supported for nested guests, but we always enable the
> +	 * secondary control for simplicity; for non-nested mode, fake that we
> +	 * didn't by injecting #UD.
> +	 */
> +	if (!is_guest_mode(vcpu)) {
> +		kvm_queue_exception(vcpu, UD_VECTOR);
> +		return 1;
> +	}
> +
> +	vmcs12 = get_vmcs12(vcpu);
> +	if ((vmcs12->vm_function_control & (1 << function)) == 0)

(learned that in c, shifting beyond the type size is undefined)

Should we check for function < 64 here? (as SDM mentions)

> +		goto fail;
> +	WARN(1, "VMCS12 VM function control should have been zero");
> +
> +fail:

We will never hit the case !nested_cpu_has_vmfunc(vmcs12) here, correct?

> +	nested_vmx_vmexit(vcpu, vmx->exit_reason,
> +			  vmcs_read32(VM_EXIT_INTR_INFO),
> +			  vmcs_readl(EXIT_QUALIFICATION));
>  	return 1;
>  }
>  


-- 

Thanks,

David