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Date: Mon, 24 Feb 2020 20:01:24 +0800
From: Xiaoyao Li <xiaoyao.li@...el.com>
To: Vitaly Kuznetsov <vkuznets@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
Paolo Bonzini <pbonzini@...hat.com>,
Sean Christopherson <sean.j.christopherson@...el.com>,
Wanpeng Li <wanpengli@...cent.com>,
Jim Mattson <jmattson@...gle.com>,
Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH 1/2] kvm: vmx: Use basic exit reason to check if it's the
specific VM EXIT
On 2/24/2020 6:16 PM, Vitaly Kuznetsov wrote:
> Xiaoyao Li <xiaoyao.li@...el.com> 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"
Ah, will correct it in v2.
>> 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@...el.com>
>> ---
>> 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.
Agreed.
>> 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.
No, we can't do this.
It's not just renaming local variable, the full 32-bit exit reason is
used elsewhere in this function that needs the upper 16-bit.
Here variable basic_exit_reason is added for the cases where only basic
exit reason number is needed.
>> 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
>
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