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

From: Xiaoyao Li
Date: Mon Feb 24 2020 - 07:01:31 EST

On 2/24/2020 6:16 PM, Vitaly Kuznetsov wrote:
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"

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@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.

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