linux-kernel - Re: [PATCH v3 2/3] KVM: nVMX: Enable VMFUNC for the L1 hypervisor

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Date:   Mon, 10 Jul 2017 22:09:43 +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 v3 2/3] KVM: nVMX: Enable VMFUNC for the L1 hypervisor


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

Should this be a WARN_ONCE?

> +
> +fail:
> +	nested_vmx_vmexit(vcpu, vmx->exit_reason,
> +			  vmcs_read32(VM_EXIT_INTR_INFO),
> +			  vmcs_readl(EXIT_QUALIFICATION));
>  	return 1;
>  }
>  
> @@ -10053,7 +10092,8 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12,
>  		exec_control &= ~(SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES |
>  				  SECONDARY_EXEC_RDTSCP |
>  				  SECONDARY_EXEC_VIRTUAL_INTR_DELIVERY |
> -				  SECONDARY_EXEC_APIC_REGISTER_VIRT);
> +				  SECONDARY_EXEC_APIC_REGISTER_VIRT |
> +				  SECONDARY_EXEC_ENABLE_VMFUNC);
>  		if (nested_cpu_has(vmcs12,
>  				   CPU_BASED_ACTIVATE_SECONDARY_CONTROLS)) {
>  			vmcs12_exec_ctrl = vmcs12->secondary_vm_exec_control &
> @@ -10061,6 +10101,10 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12,
>  			exec_control |= vmcs12_exec_ctrl;
>  		}
>  
> +		/* All VMFUNCs are currently emulated through L0 vmexits.  */
> +		if (exec_control & SECONDARY_EXEC_ENABLE_VMFUNC)
> +			vmcs_write64(VM_FUNCTION_CONTROL, 0);
> +
>  		if (exec_control & SECONDARY_EXEC_VIRTUAL_INTR_DELIVERY) {
>  			vmcs_write64(EOI_EXIT_BITMAP0,
>  				vmcs12->eoi_exit_bitmap0);
> @@ -10310,6 +10354,11 @@ static int check_vmentry_prereqs(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
>  				vmx->nested.nested_vmx_entry_ctls_high))
>  		return VMXERR_ENTRY_INVALID_CONTROL_FIELD;
>  
> +	if (nested_cpu_has_vmfunc(vmcs12) &&
> +	    (vmcs12->vm_function_control &
> +	     ~vmx->nested.nested_vmx_vmfunc_controls))

I'd prefer the second part on one line, although it will violate 80
chars. (these variable names really start to get too lengthy to be useful)

> +		return VMXERR_ENTRY_INVALID_CONTROL_FIELD;
> +
>  	if (vmcs12->cr3_target_count > nested_cpu_vmx_misc_cr3_count(vcpu))
>  		return VMXERR_ENTRY_INVALID_CONTROL_FIELD;
>  
> 

Feel free to ignore my comments.

Reviewed-by: David Hildenbrand <david@...hat.com>


-- 

Thanks,

David