Re: [PATCH 1/2] kvm: vmx: Use basic exit reason to check if it's the specific VM EXIT
From: Krish Sadhukhan
Date: Mon Feb 24 2020 - 19:28:59 EST
On 02/24/2020 04:01 AM, Xiaoyao Li wrote:
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)
ÂÂÂÂÂÂ * i.e. we end up advancing IP with some random value.
ÂÂÂÂÂÂ */
ÂÂÂÂÂ if (!static_cpu_has(X86_FEATURE_HYPERVISOR) ||
-ÂÂÂÂÂÂÂ to_vmx(vcpu)->exit_reason != EXIT_REASON_EPT_MISCONFIG) {
+ÂÂÂÂÂÂÂ 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.
ÂÂÂÂÂÂÂÂÂ rip = kvm_rip_read(vcpu);
ÂÂÂÂÂÂÂÂÂ rip += vmcs_read32(VM_EXIT_INSTRUCTION_LEN);
ÂÂÂÂÂÂÂÂÂ kvm_rip_write(vcpu, rip);
@@ -5797,6 +5797,7 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu,
 {
ÂÂÂÂÂ struct vcpu_vmx *vmx = to_vmx(vcpu);
ÂÂÂÂÂ u32 exit_reason = vmx->exit_reason;
+ÂÂÂ 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.
ÂÂÂÂÂ u32 vectoring_info = vmx->idt_vectoring_info;
 Â trace_kvm_exit(exit_reason, vcpu, KVM_ISA_VMX);
@@ -5842,17 +5843,17 @@ static int vmx_handle_exit(struct kvm_vcpu
*vcpu,
ÂÂÂÂÂÂ * will cause infinite loop.
ÂÂÂÂÂÂ */
ÂÂÂÂÂ if ((vectoring_info & VECTORING_INFO_VALID_MASK) &&
-ÂÂÂÂÂÂÂÂÂÂÂ (exit_reason != EXIT_REASON_EXCEPTION_NMI &&
-ÂÂÂÂÂÂÂÂÂÂÂ exit_reason != EXIT_REASON_EPT_VIOLATION &&
-ÂÂÂÂÂÂÂÂÂÂÂ exit_reason != EXIT_REASON_PML_FULL &&
-ÂÂÂÂÂÂÂÂÂÂÂ exit_reason != EXIT_REASON_TASK_SWITCH)) {
+ÂÂÂÂÂÂÂÂÂÂÂ (basic_exit_reason != EXIT_REASON_EXCEPTION_NMI &&
+ÂÂÂÂÂÂÂÂÂÂÂÂ basic_exit_reason != EXIT_REASON_EPT_VIOLATION &&
+ÂÂÂÂÂÂÂÂÂÂÂÂ basic_exit_reason != EXIT_REASON_PML_FULL &&
+ÂÂÂÂÂÂÂÂÂÂÂÂ basic_exit_reason != EXIT_REASON_TASK_SWITCH)) {
ÂÂÂÂÂÂÂÂÂ vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
ÂÂÂÂÂÂÂÂÂ vcpu->run->internal.suberror =
KVM_INTERNAL_ERROR_DELIVERY_EV;
ÂÂÂÂÂÂÂÂÂ vcpu->run->internal.ndata = 3;
ÂÂÂÂÂÂÂÂÂ vcpu->run->internal.data[0] = vectoring_info;
ÂÂÂÂÂÂÂÂÂ vcpu->run->internal.data[1] = exit_reason;
ÂÂÂÂÂÂÂÂÂ vcpu->run->internal.data[2] = vcpu->arch.exit_qualification;
-ÂÂÂÂÂÂÂ if (exit_reason == EXIT_REASON_EPT_MISCONFIG) {
+ÂÂÂÂÂÂÂ if (basic_exit_reason == EXIT_REASON_EPT_MISCONFIG) {
ÂÂÂÂÂÂÂÂÂÂÂÂÂ vcpu->run->internal.ndata++;
ÂÂÂÂÂÂÂÂÂÂÂÂÂ vcpu->run->internal.data[3] =
ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ vmcs_read64(GUEST_PHYSICAL_ADDRESS);
@@ -5884,32 +5885,32 @@ static int vmx_handle_exit(struct kvm_vcpu
*vcpu,
ÂÂÂÂÂÂÂÂÂ return 1;
ÂÂÂÂÂ }
 - if (exit_reason >= kvm_vmx_max_exit_handlers)
+ÂÂÂ if (basic_exit_reason >= kvm_vmx_max_exit_handlers)
ÂÂÂÂÂÂÂÂÂ goto unexpected_vmexit;
 #ifdef CONFIG_RETPOLINE
-ÂÂÂ if (exit_reason == EXIT_REASON_MSR_WRITE)
+ÂÂÂ if (basic_exit_reason == EXIT_REASON_MSR_WRITE)
ÂÂÂÂÂÂÂÂÂ return kvm_emulate_wrmsr(vcpu);
-ÂÂÂ else if (exit_reason == EXIT_REASON_PREEMPTION_TIMER)
+ÂÂÂ else if (basic_exit_reason == EXIT_REASON_PREEMPTION_TIMER)
ÂÂÂÂÂÂÂÂÂ return handle_preemption_timer(vcpu);
-ÂÂÂ else if (exit_reason == EXIT_REASON_INTERRUPT_WINDOW)
+ÂÂÂ else if (basic_exit_reason == EXIT_REASON_INTERRUPT_WINDOW)
ÂÂÂÂÂÂÂÂÂ return handle_interrupt_window(vcpu);
-ÂÂÂ else if (exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT)
+ÂÂÂ else if (basic_exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT)
ÂÂÂÂÂÂÂÂÂ return handle_external_interrupt(vcpu);
-ÂÂÂ else if (exit_reason == EXIT_REASON_HLT)
+ÂÂÂ else if (basic_exit_reason == EXIT_REASON_HLT)
ÂÂÂÂÂÂÂÂÂ return kvm_emulate_halt(vcpu);
-ÂÂÂ else if (exit_reason == EXIT_REASON_EPT_MISCONFIG)
+ÂÂÂ else if (basic_exit_reason == EXIT_REASON_EPT_MISCONFIG)
ÂÂÂÂÂÂÂÂÂ return handle_ept_misconfig(vcpu);
 #endif
 - exit_reason = array_index_nospec(exit_reason,
+ÂÂÂ basic_exit_reason = array_index_nospec(basic_exit_reason,
ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ kvm_vmx_max_exit_handlers);
-ÂÂÂ if (!kvm_vmx_exit_handlers[exit_reason])
+ÂÂÂ if (!kvm_vmx_exit_handlers[basic_exit_reason])
ÂÂÂÂÂÂÂÂÂ goto unexpected_vmexit;
 - return kvm_vmx_exit_handlers[exit_reason](vcpu);
+ÂÂÂ return kvm_vmx_exit_handlers[basic_exit_reason](vcpu);
  unexpected_vmexit:
-ÂÂÂ vcpu_unimpl(vcpu, "vmx: unexpected exit reason 0x%x\n",
exit_reason);
+ÂÂÂ vcpu_unimpl(vcpu, "vmx: unexpected exit reason 0x%x\n",
basic_exit_reason);
ÂÂÂÂÂ dump_vmcs();
ÂÂÂÂÂ vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
ÂÂÂÂÂ vcpu->run->internal.suberror =
@@ -6241,13 +6242,14 @@ static void vmx_handle_exit_irqoff(struct
kvm_vcpu *vcpu,
ÂÂÂÂÂ enum exit_fastpath_completion *exit_fastpath)
 {
ÂÂÂÂÂ struct vcpu_vmx *vmx = to_vmx(vcpu);
+ÂÂÂ 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)
+ÂÂÂ if (basic_exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT)
ÂÂÂÂÂÂÂÂÂ handle_external_interrupt_irqoff(vcpu);
-ÂÂÂ else if (vmx->exit_reason == EXIT_REASON_EXCEPTION_NMI)
+ÂÂÂ else if (basic_exit_reason == EXIT_REASON_EXCEPTION_NMI)
ÂÂÂÂÂÂÂÂÂ handle_exception_nmi_irqoff(vmx);
ÂÂÂÂÂ else if (!is_guest_mode(vcpu) &&
-ÂÂÂÂÂÂÂ vmx->exit_reason == EXIT_REASON_MSR_WRITE)
+ÂÂÂÂÂÂÂÂ basic_exit_reason == EXIT_REASON_MSR_WRITE)
ÂÂÂÂÂÂÂÂÂ *exit_fastpath = handle_fastpath_set_msr_irqoff(vcpu);
 }
 @@ -6621,7 +6623,7 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu)
ÂÂÂÂÂ vmx->idt_vectoring_info = 0;
 Â vmx->exit_reason = vmx->fail ? 0xdead :
vmcs_read32(VM_EXIT_REASON);
-ÂÂÂ if ((u16)vmx->exit_reason == EXIT_REASON_MCE_DURING_VMENTRY)
+ÂÂÂ if (basic(vmx->exit_reason) == EXIT_REASON_MCE_DURING_VMENTRY)
ÂÂÂÂÂÂÂÂÂ kvm_machine_check();
 Â 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))
We have a macro for bit 31,
ÂÂÂ VMX_EXIT_REASONS_FAILED_VMENTRYÂÂÂ ÂÂÂ ÂÂÂ ÂÂÂ 0x80000000
Does it make sense to define a macro like that instead ? Say,
ÂÂÂ VMX_BASIC_EXIT_REASONÂÂÂ ÂÂÂ 0x0000ffff
and then we do,
ÂÂÂ u32 exit_reason = vmx->exit_reason;
ÂÂÂ u16 basic_exit_reason = exit_reason & VMX_BASIC_EXIT_REASON;
+
 #ifdef CONFIG_X86_64
 #define NR_SHARED_MSRS 7
 #else