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Subject[PATCH 10/10] KVM: VMX: Convert vcpu_vmx.exit_reason to a union
Date
Convert vcpu_vmx.exit_reason from a u32 to a union (of size u32).  The
full VM_EXIT_REASON field is comprised of a 16-bit basic exit reason in
bits 15:0, and single-bit modifiers in bits 31:16.

Historically, KVM has only had to worry about handling the "failed
VM-Entry" modifier, which could only be set in very specific flows and
required dedicated handling. I.e. manually stripping the FAILED_VMENTRY
bit was a somewhat viable approach. But even with only a single bit to
worry about, KVM has had several bugs related to comparing a basic exit
reason against the full exit reason stored in vcpu_vmx.

Upcoming Intel features, e.g. SGX, will add new modifier bits that can
be set on more or less any VM-Exit, as opposed to the significantly more
restricted FAILED_VMENTRY, i.e. correctly handling everything in one-off
flows isn't scalable. Tracking exit reason in a union forces code to
explicitly choose between consuming the full exit reason and the basic
exit reason, and is a convenient way to document and access the
modifiers.

No functional change intended.

Cc: Xiaoyao Li <xiaoyao.li@intel.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
arch/x86/kvm/vmx/nested.c | 11 ++++++++---
arch/x86/kvm/vmx/nested.h | 2 +-
arch/x86/kvm/vmx/vmx.c | 24 ++++++++++++------------
arch/x86/kvm/vmx/vmx.h | 25 ++++++++++++++++++++++++-
4 files changed, 45 insertions(+), 17 deletions(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index c775feca3eb0..0c7cea35dd33 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -5307,7 +5307,12 @@ static int handle_vmfunc(struct kvm_vcpu *vcpu)
return kvm_skip_emulated_instruction(vcpu);

fail:
- nested_vmx_vmexit(vcpu, vmx->exit_reason,
+ /*
+ * This is effectively a reflected VM-Exit, as opposed to a synthesized
+ * nested VM-Exit. Pass the original exit reason, i.e. don't hardcode
+ * EXIT_REASON_VMFUNC as the exit reason.
+ */
+ nested_vmx_vmexit(vcpu, vmx->exit_reason.full,
vmcs_read32(VM_EXIT_INTR_INFO),
vmcs_readl(EXIT_QUALIFICATION));
return 1;
@@ -5549,14 +5554,14 @@ bool nested_vmx_exit_reflected(struct kvm_vcpu *vcpu)
*/
nested_mark_vmcs12_pages_dirty(vcpu);

- trace_kvm_nested_vmexit(kvm_rip_read(vcpu), vmx->exit_reason,
+ trace_kvm_nested_vmexit(kvm_rip_read(vcpu), vmx->exit_reason.full,
vmcs_readl(EXIT_QUALIFICATION),
vmx->idt_vectoring_info,
intr_info,
vmcs_read32(VM_EXIT_INTR_ERROR_CODE),
KVM_ISA_VMX);

- exit_reason = vmx->exit_reason;
+ exit_reason = vmx->exit_reason.basic;

switch (exit_reason) {
case EXIT_REASON_EXCEPTION_NMI:
diff --git a/arch/x86/kvm/vmx/nested.h b/arch/x86/kvm/vmx/nested.h
index 04584bcbcc8d..07ce09f88977 100644
--- a/arch/x86/kvm/vmx/nested.h
+++ b/arch/x86/kvm/vmx/nested.h
@@ -98,7 +98,7 @@ static inline bool nested_vmx_reflect_vmexit(struct kvm_vcpu *vcpu)
vmcs_read32(VM_EXIT_INTR_ERROR_CODE);
}

- nested_vmx_vmexit(vcpu, to_vmx(vcpu)->exit_reason, exit_intr_info,
+ nested_vmx_vmexit(vcpu, to_vmx(vcpu)->exit_reason.full, exit_intr_info,
vmcs_readl(EXIT_QUALIFICATION));
return true;
}
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 910a7cadeaf7..521b99f63608 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1588,7 +1588,7 @@ 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) {
+ to_vmx(vcpu)->exit_reason.basic != EXIT_REASON_EPT_MISCONFIG) {
rip = kvm_rip_read(vcpu);
rip += vmcs_read32(VM_EXIT_INSTRUCTION_LEN);
kvm_rip_write(vcpu, rip);
@@ -5847,7 +5847,7 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu,
u32 vectoring_info = vmx->idt_vectoring_info;
u16 exit_reason;

- trace_kvm_exit(vmx->exit_reason, vcpu, KVM_ISA_VMX);
+ trace_kvm_exit(vmx->exit_reason.full, vcpu, KVM_ISA_VMX);

/*
* Flush logged GPAs PML buffer, this will make dirty_bitmap more
@@ -5866,11 +5866,11 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu,
if (is_guest_mode(vcpu) && nested_vmx_reflect_vmexit(vcpu))
return 1;

- if (vmx->exit_reason & VMX_EXIT_REASONS_FAILED_VMENTRY) {
+ if (vmx->exit_reason.failed_vmentry) {
dump_vmcs();
vcpu->run->exit_reason = KVM_EXIT_FAIL_ENTRY;
vcpu->run->fail_entry.hardware_entry_failure_reason
- = vmx->exit_reason;
+ = vmx->exit_reason.full;
return 0;
}

@@ -5882,7 +5882,7 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu,
return 0;
}

- exit_reason = vmx->exit_reason;
+ exit_reason = vmx->exit_reason.basic;

/*
* Note:
@@ -5900,7 +5900,7 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu,
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] = vmx->exit_reason;
+ vcpu->run->internal.data[1] = vmx->exit_reason.full;
vcpu->run->internal.data[2] = vcpu->arch.exit_qualification;
if (exit_reason == EXIT_REASON_EPT_MISCONFIG) {
vcpu->run->internal.ndata++;
@@ -5960,13 +5960,13 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu,

unexpected_vmexit:
vcpu_unimpl(vcpu, "vmx: unexpected exit reason 0x%x\n",
- vmx->exit_reason);
+ vmx->exit_reason.full);
dump_vmcs();
vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
vcpu->run->internal.suberror =
KVM_INTERNAL_ERROR_UNEXPECTED_EXIT_REASON;
vcpu->run->internal.ndata = 1;
- vcpu->run->internal.data[0] = vmx->exit_reason;
+ vcpu->run->internal.data[0] = vmx->exit_reason.full;
return 0;
}

@@ -6290,7 +6290,7 @@ static void vmx_handle_exit_irqoff(struct kvm_vcpu *vcpu,
enum exit_fastpath_completion *exit_fastpath)
{
struct vcpu_vmx *vmx = to_vmx(vcpu);
- u16 exit_reason = vmx->exit_reason;
+ u16 exit_reason = vmx->exit_reason.basic;

if (exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT)
handle_external_interrupt_irqoff(vcpu);
@@ -6672,11 +6672,11 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu)
vmx->nested.nested_run_pending = 0;
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)
+ vmx->exit_reason.full = vmx->fail ? 0xdead : vmcs_read32(VM_EXIT_REASON);
+ if (vmx->exit_reason.basic == EXIT_REASON_MCE_DURING_VMENTRY)
kvm_machine_check();

- if (vmx->fail || (vmx->exit_reason & VMX_EXIT_REASONS_FAILED_VMENTRY))
+ if (vmx->fail || vmx->exit_reason.failed_vmentry)
return;

vmx->loaded_vmcs->launched = 1;
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index e64da06c7009..2d9a005d11ab 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -93,6 +93,29 @@ struct pt_desc {
struct pt_ctx guest;
};

+union vmx_exit_reason {
+ struct {
+ u32 basic : 16;
+ u32 reserved16 : 1;
+ u32 reserved17 : 1;
+ u32 reserved18 : 1;
+ u32 reserved19 : 1;
+ u32 reserved20 : 1;
+ u32 reserved21 : 1;
+ u32 reserved22 : 1;
+ u32 reserved23 : 1;
+ u32 reserved24 : 1;
+ u32 reserved25 : 1;
+ u32 reserved26 : 1;
+ u32 enclave_mode : 1;
+ u32 smi_pending_mtf : 1;
+ u32 smi_from_vmx_root : 1;
+ u32 reserved30 : 1;
+ u32 failed_vmentry : 1;
+ };
+ u32 full;
+};
+
/*
* The nested_vmx structure is part of vcpu_vmx, and holds information we need
* for correct emulation of VMX (i.e., nested VMX) on this vcpu.
@@ -263,7 +286,7 @@ struct vcpu_vmx {
int vpid;
bool emulation_required;

- u32 exit_reason;
+ union vmx_exit_reason exit_reason;

/* Posted interrupt descriptor */
struct pi_desc pi_desc;
--
2.24.1
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