Re: [PATCH 1/2] kvm: vmx: Use basic exit reason to check if it's the specific VM EXIT

[Vitaly Kuznetsov]

Xiaoyao Li <xiaoyao.li@xxxxxxxxx> writes:

> Current kvm uses the 32-bit exit reason to check if it's any specific VM
> EXIT, however only the low 16-bit of VM EXIT REASON acts as the basic
> exit reason.
>
> Introduce Macro basic(exit_reaso)

"exit_reason"

>  to help retrieve the basic exit reason
> from VM EXIT REASON, and use the basic exit reason for checking and
> indexing the exit hanlder.
>
> Signed-off-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
> ---
>  arch/x86/kvm/vmx/vmx.c | 44 ++++++++++++++++++++++--------------------
>  arch/x86/kvm/vmx/vmx.h |  2 ++
>  2 files changed, 25 insertions(+), 21 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 9a6664886f2e..85da72d4dc92 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -1584,7 +1584,7 @@ static int skip_emulated_instruction(struct kvm_vcpu *vcpu)
>  	 * i.e. we end up advancing IP with some random value.
>  	 */
>  	if (!static_cpu_has(X86_FEATURE_HYPERVISOR) ||
> -	    to_vmx(vcpu)->exit_reason != EXIT_REASON_EPT_MISCONFIG) {
> +	    basic(to_vmx(vcpu)->exit_reason) != EXIT_REASON_EPT_MISCONFIG) {

"basic" word is probably 'too basic' to be used for this purpose. Even
if we need a macro for it (I'm not really convinced it improves the
readability), I'd suggest we name it 'basic_exit_reason()' instead.

>  		rip = kvm_rip_read(vcpu);
>  		rip += vmcs_read32(VM_EXIT_INSTRUCTION_LEN);
>  		kvm_rip_write(vcpu, rip);
> @@ -5797,6 +5797,7 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu,
>  {
>  	struct vcpu_vmx *vmx = to_vmx(vcpu);
>  	u32 exit_reason = vmx->exit_reason;
> +	u16 basic_exit_reason = basic(exit_reason);

I don't think renaming local variable is needed, let's just do

'u16 exit_reason = basic_exit_reason(vmx->exit_reason)' and keep the
rest of the code as-is.

>  	u32 vectoring_info = vmx->idt_vectoring_info;
>  
>  	trace_kvm_exit(exit_reason, vcpu, KVM_ISA_VMX);
> @@ -5842,17 +5843,17 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu,
>  	 * will cause infinite loop.
>  	 */
>  	if ((vectoring_info & VECTORING_INFO_VALID_MASK) &&
> -			(exit_reason != EXIT_REASON_EXCEPTION_NMI &&
> -			exit_reason != EXIT_REASON_EPT_VIOLATION &&
> -			exit_reason != EXIT_REASON_PML_FULL &&
> -			exit_reason != EXIT_REASON_TASK_SWITCH)) {
> +			(basic_exit_reason != EXIT_REASON_EXCEPTION_NMI &&
> +			 basic_exit_reason != EXIT_REASON_EPT_VIOLATION &&
> +			 basic_exit_reason != EXIT_REASON_PML_FULL &&
> +			 basic_exit_reason != EXIT_REASON_TASK_SWITCH)) {
>  		vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
>  		vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_DELIVERY_EV;
>  		vcpu->run->internal.ndata = 3;
>  		vcpu->run->internal.data[0] = vectoring_info;
>  		vcpu->run->internal.data[1] = exit_reason;
>  		vcpu->run->internal.data[2] = vcpu->arch.exit_qualification;
> -		if (exit_reason == EXIT_REASON_EPT_MISCONFIG) {
> +		if (basic_exit_reason == EXIT_REASON_EPT_MISCONFIG) {
>  			vcpu->run->internal.ndata++;
>  			vcpu->run->internal.data[3] =
>  				vmcs_read64(GUEST_PHYSICAL_ADDRESS);
> @@ -5884,32 +5885,32 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu,
>  		return 1;
>  	}
>  
> -	if (exit_reason >= kvm_vmx_max_exit_handlers)
> +	if (basic_exit_reason >= kvm_vmx_max_exit_handlers)
>  		goto unexpected_vmexit;
>  #ifdef CONFIG_RETPOLINE
> -	if (exit_reason == EXIT_REASON_MSR_WRITE)
> +	if (basic_exit_reason == EXIT_REASON_MSR_WRITE)
>  		return kvm_emulate_wrmsr(vcpu);
> -	else if (exit_reason == EXIT_REASON_PREEMPTION_TIMER)
> +	else if (basic_exit_reason == EXIT_REASON_PREEMPTION_TIMER)
>  		return handle_preemption_timer(vcpu);
> -	else if (exit_reason == EXIT_REASON_INTERRUPT_WINDOW)
> +	else if (basic_exit_reason == EXIT_REASON_INTERRUPT_WINDOW)
>  		return handle_interrupt_window(vcpu);
> -	else if (exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT)
> +	else if (basic_exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT)
>  		return handle_external_interrupt(vcpu);
> -	else if (exit_reason == EXIT_REASON_HLT)
> +	else if (basic_exit_reason == EXIT_REASON_HLT)
>  		return kvm_emulate_halt(vcpu);
> -	else if (exit_reason == EXIT_REASON_EPT_MISCONFIG)
> +	else if (basic_exit_reason == EXIT_REASON_EPT_MISCONFIG)
>  		return handle_ept_misconfig(vcpu);
>  #endif
>  
> -	exit_reason = array_index_nospec(exit_reason,
> +	basic_exit_reason = array_index_nospec(basic_exit_reason,
>  					 kvm_vmx_max_exit_handlers);
> -	if (!kvm_vmx_exit_handlers[exit_reason])
> +	if (!kvm_vmx_exit_handlers[basic_exit_reason])
>  		goto unexpected_vmexit;
>  
> -	return kvm_vmx_exit_handlers[exit_reason](vcpu);
> +	return kvm_vmx_exit_handlers[basic_exit_reason](vcpu);
>  
>  unexpected_vmexit:
> -	vcpu_unimpl(vcpu, "vmx: unexpected exit reason 0x%x\n", exit_reason);
> +	vcpu_unimpl(vcpu, "vmx: unexpected exit reason 0x%x\n", basic_exit_reason);
>  	dump_vmcs();
>  	vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
>  	vcpu->run->internal.suberror =
> @@ -6241,13 +6242,14 @@ static void vmx_handle_exit_irqoff(struct kvm_vcpu *vcpu,
>  	enum exit_fastpath_completion *exit_fastpath)
>  {
>  	struct vcpu_vmx *vmx = to_vmx(vcpu);
> +	u16 basic_exit_reason = basic(vmx->exit_reason);

Here I'd suggest we also use the same 

'u16 exit_reason = basic_exit_reason(vmx->exit_reason)'

as above.

>  
> -	if (vmx->exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT)
> +	if (basic_exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT)
>  		handle_external_interrupt_irqoff(vcpu);
> -	else if (vmx->exit_reason == EXIT_REASON_EXCEPTION_NMI)
> +	else if (basic_exit_reason == EXIT_REASON_EXCEPTION_NMI)
>  		handle_exception_nmi_irqoff(vmx);
>  	else if (!is_guest_mode(vcpu) &&
> -		vmx->exit_reason == EXIT_REASON_MSR_WRITE)
> +		 basic_exit_reason == EXIT_REASON_MSR_WRITE)
>  		*exit_fastpath = handle_fastpath_set_msr_irqoff(vcpu);
>  }
>  
> @@ -6621,7 +6623,7 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu)
>  	vmx->idt_vectoring_info = 0;
>  
>  	vmx->exit_reason = vmx->fail ? 0xdead : vmcs_read32(VM_EXIT_REASON);
> -	if ((u16)vmx->exit_reason == EXIT_REASON_MCE_DURING_VMENTRY)
> +	if (basic(vmx->exit_reason) == EXIT_REASON_MCE_DURING_VMENTRY)
>  		kvm_machine_check();
>  
>  	if (vmx->fail || (vmx->exit_reason & VMX_EXIT_REASONS_FAILED_VMENTRY))
> diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
> index 7f42cf3dcd70..c6ba33eedb59 100644
> --- a/arch/x86/kvm/vmx/vmx.h
> +++ b/arch/x86/kvm/vmx/vmx.h
> @@ -22,6 +22,8 @@ extern u32 get_umwait_control_msr(void);
>  
>  #define X2APIC_MSR(r) (APIC_BASE_MSR + ((r) >> 4))
>  
> +#define basic(exit_reason) ((u16)(exit_reason))
> +
>  #ifdef CONFIG_X86_64
>  #define NR_SHARED_MSRS	7
>  #else

-- 
Vitaly