[RFC PATCH v3 16/27] KVM: VMX: Convert vcpu_vmx.exit_reason to a union

Kai Huang
2021-01-26T15:32:12Z

From: Sean Christopherson <sean.j.christopherson@intel.com>

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 store 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, and is a convenient way to document and access the modifiers.

No functional change intended.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Kai Huang <kai.huang@intel.com>
---
arch/x86/kvm/vmx/nested.c | 42 +++++++++++++++---------
arch/x86/kvm/vmx/vmx.c | 68 ++++++++++++++++++++-------------------
arch/x86/kvm/vmx/vmx.h | 25 +++++++++++++-
3 files changed, 86 insertions(+), 49 deletions(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 0fbb46990dfc..f112c2482887 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -3311,7 +3311,11 @@ enum nvmx_vmentry_status nested_vmx_enter_non_root_mode(struct kvm_vcpu *vcpu,
struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
enum vm_entry_failure_code entry_failure_code;
bool evaluate_pending_interrupts;
- u32 exit_reason, failed_index;
+ u32 failed_index;
+ union vmx_exit_reason exit_reason = {
+ .basic = -1,
+ .failed_vmentry = 1,
+ };

if (kvm_check_request(KVM_REQ_TLB_FLUSH_CURRENT, vcpu))
kvm_vcpu_flush_tlb_current(vcpu);
@@ -3363,7 +3367,7 @@ enum nvmx_vmentry_status nested_vmx_enter_non_root_mode(struct kvm_vcpu *vcpu,

if (nested_vmx_check_guest_state(vcpu, vmcs12,
&entry_failure_code)) {
- exit_reason = EXIT_REASON_INVALID_STATE;
+ exit_reason.basic = EXIT_REASON_INVALID_STATE;
vmcs12->exit_qualification = entry_failure_code;
goto vmentry_fail_vmexit;
}
@@ -3374,7 +3378,7 @@ enum nvmx_vmentry_status nested_vmx_enter_non_root_mode(struct kvm_vcpu *vcpu,
vcpu->arch.tsc_offset += vmcs12->tsc_offset;

if (prepare_vmcs02(vcpu, vmcs12, &entry_failure_code)) {
- exit_reason = EXIT_REASON_INVALID_STATE;
+ exit_reason.basic = EXIT_REASON_INVALID_STATE;
vmcs12->exit_qualification = entry_failure_code;
goto vmentry_fail_vmexit_guest_mode;
}
@@ -3384,7 +3388,7 @@ enum nvmx_vmentry_status nested_vmx_enter_non_root_mode(struct kvm_vcpu *vcpu,
vmcs12->vm_entry_msr_load_addr,
vmcs12->vm_entry_msr_load_count);
if (failed_index) {
- exit_reason = EXIT_REASON_MSR_LOAD_FAIL;
+ exit_reason.basic = EXIT_REASON_MSR_LOAD_FAIL;
vmcs12->exit_qualification = failed_index;
goto vmentry_fail_vmexit_guest_mode;
}
@@ -3452,7 +3456,7 @@ enum nvmx_vmentry_status nested_vmx_enter_non_root_mode(struct kvm_vcpu *vcpu,
return NVMX_VMENTRY_VMEXIT;

load_vmcs12_host_state(vcpu, vmcs12);
- vmcs12->vm_exit_reason = exit_reason | VMX_EXIT_REASONS_FAILED_VMENTRY;
+ vmcs12->vm_exit_reason = exit_reason.full;
if (enable_shadow_vmcs || vmx->nested.hv_evmcs)
vmx->nested.need_vmcs12_to_shadow_sync = true;
return NVMX_VMENTRY_VMEXIT;
@@ -5540,7 +5544,12 @@ 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,
vmx_get_intr_info(vcpu),
vmx_get_exit_qual(vcpu));
return 1;
@@ -5608,7 +5617,8 @@ static bool nested_vmx_exit_handled_io(struct kvm_vcpu *vcpu,
* MSR bitmap. This may be the case even when L0 doesn't use MSR bitmaps.
*/
static bool nested_vmx_exit_handled_msr(struct kvm_vcpu *vcpu,
- struct vmcs12 *vmcs12, u32 exit_reason)
+ struct vmcs12 *vmcs12,
+ union vmx_exit_reason exit_reason)
{
u32 msr_index = kvm_rcx_read(vcpu);
gpa_t bitmap;
@@ -5622,7 +5632,7 @@ static bool nested_vmx_exit_handled_msr(struct kvm_vcpu *vcpu,
* First we need to figure out which of the four to use:
*/
bitmap = vmcs12->msr_bitmap;
- if (exit_reason == EXIT_REASON_MSR_WRITE)
+ if (exit_reason.basic == EXIT_REASON_MSR_WRITE)
bitmap += 2048;
if (msr_index >= 0xc0000000) {
msr_index -= 0xc0000000;
@@ -5759,11 +5769,12 @@ static bool nested_vmx_exit_handled_mtf(struct vmcs12 *vmcs12)
* Return true if L0 wants to handle an exit from L2 regardless of whether or not
* L1 wants the exit. Only call this when in is_guest_mode (L2).
*/
-static bool nested_vmx_l0_wants_exit(struct kvm_vcpu *vcpu, u32 exit_reason)
+static bool nested_vmx_l0_wants_exit(struct kvm_vcpu *vcpu,
+ union vmx_exit_reason exit_reason)
{
u32 intr_info;

- switch ((u16)exit_reason) {
+ switch (exit_reason.basic) {
case EXIT_REASON_EXCEPTION_NMI:
intr_info = vmx_get_intr_info(vcpu);
if (is_nmi(intr_info))
@@ -5819,12 +5830,13 @@ static bool nested_vmx_l0_wants_exit(struct kvm_vcpu *vcpu, u32 exit_reason)
* Return 1 if L1 wants to intercept an exit from L2. Only call this when in
* is_guest_mode (L2).
*/
-static bool nested_vmx_l1_wants_exit(struct kvm_vcpu *vcpu, u32 exit_reason)
+static bool nested_vmx_l1_wants_exit(struct kvm_vcpu *vcpu,
+ union vmx_exit_reason exit_reason)
{
struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
u32 intr_info;

- switch ((u16)exit_reason) {
+ switch (exit_reason.basic) {
case EXIT_REASON_EXCEPTION_NMI:
intr_info = vmx_get_intr_info(vcpu);
if (is_nmi(intr_info))
@@ -5943,7 +5955,7 @@ static bool nested_vmx_l1_wants_exit(struct kvm_vcpu *vcpu, u32 exit_reason)
bool nested_vmx_reflect_vmexit(struct kvm_vcpu *vcpu)
{
struct vcpu_vmx *vmx = to_vmx(vcpu);
- u32 exit_reason = vmx->exit_reason;
+ union vmx_exit_reason exit_reason = vmx->exit_reason;
unsigned long exit_qual;
u32 exit_intr_info;

@@ -5962,7 +5974,7 @@ bool nested_vmx_reflect_vmexit(struct kvm_vcpu *vcpu)
goto reflect_vmexit;
}

- trace_kvm_nested_vmexit(exit_reason, vcpu, KVM_ISA_VMX);
+ trace_kvm_nested_vmexit(exit_reason.full, vcpu, KVM_ISA_VMX);

/* If L0 (KVM) wants the exit, it trumps L1's desires. */
if (nested_vmx_l0_wants_exit(vcpu, exit_reason))
@@ -5988,7 +6000,7 @@ bool nested_vmx_reflect_vmexit(struct kvm_vcpu *vcpu)
exit_qual = vmx_get_exit_qual(vcpu);

reflect_vmexit:
- nested_vmx_vmexit(vcpu, exit_reason, exit_intr_info, exit_qual);
+ nested_vmx_vmexit(vcpu, exit_reason.full, exit_intr_info, exit_qual);
return true;
}

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 2af05d3b0590..746b87375aff 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1577,7 +1577,7 @@ 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) {
orig_rip = kvm_rip_read(vcpu);
rip = orig_rip + vmcs_read32(VM_EXIT_INSTRUCTION_LEN);
#ifdef CONFIG_X86_64
@@ -5667,7 +5667,7 @@ static void vmx_get_exit_info(struct kvm_vcpu *vcpu, u64 *info1, u64 *info2,
struct vcpu_vmx *vmx = to_vmx(vcpu);

*info1 = vmx_get_exit_qual(vcpu);
- if (!(vmx->exit_reason & VMX_EXIT_REASONS_FAILED_VMENTRY)) {
+ if (!vmx->exit_reason.failed_vmentry) {
*info2 = vmx->idt_vectoring_info;
*intr_info = vmx_get_intr_info(vcpu);
if (is_exception_with_error_code(*intr_info))
@@ -5911,8 +5911,9 @@ void dump_vmcs(void)
static int vmx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t exit_fastpath)
{
struct vcpu_vmx *vmx = to_vmx(vcpu);
- u32 exit_reason = vmx->exit_reason;
+ union vmx_exit_reason exit_reason = vmx->exit_reason;
u32 vectoring_info = vmx->idt_vectoring_info;
+ u16 exit_handler_index;

/*
* Flush logged GPAs PML buffer, this will make dirty_bitmap more
@@ -5954,11 +5955,11 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t exit_fastpath)
return 1;
}

- if (exit_reason & VMX_EXIT_REASONS_FAILED_VMENTRY) {
+ if (exit_reason.failed_vmentry) {
dump_vmcs();
vcpu->run->exit_reason = KVM_EXIT_FAIL_ENTRY;
vcpu->run->fail_entry.hardware_entry_failure_reason
- = exit_reason;
+ = exit_reason.full;
vcpu->run->fail_entry.cpu = vcpu->arch.last_vmentry_cpu;
return 0;
}
@@ -5980,18 +5981,18 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t exit_fastpath)
* 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_APIC_ACCESS &&
- exit_reason != EXIT_REASON_TASK_SWITCH)) {
+ (exit_reason.basic != EXIT_REASON_EXCEPTION_NMI &&
+ exit_reason.basic != EXIT_REASON_EPT_VIOLATION &&
+ exit_reason.basic != EXIT_REASON_PML_FULL &&
+ exit_reason.basic != EXIT_REASON_APIC_ACCESS &&
+ exit_reason.basic != 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[1] = exit_reason.full;
vcpu->run->internal.data[2] = vcpu->arch.exit_qualification;
- if (exit_reason == EXIT_REASON_EPT_MISCONFIG) {
+ if (exit_reason.basic == EXIT_REASON_EPT_MISCONFIG) {
vcpu->run->internal.ndata++;
vcpu->run->internal.data[3] =
vmcs_read64(GUEST_PHYSICAL_ADDRESS);
@@ -6023,38 +6024,39 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t exit_fastpath)
if (exit_fastpath != EXIT_FASTPATH_NONE)
return 1;

- if (exit_reason >= kvm_vmx_max_exit_handlers)
+ if (exit_reason.basic >= kvm_vmx_max_exit_handlers)
goto unexpected_vmexit;
#ifdef CONFIG_RETPOLINE
- if (exit_reason == EXIT_REASON_MSR_WRITE)
+ if (exit_reason.basic == EXIT_REASON_MSR_WRITE)
return kvm_emulate_wrmsr(vcpu);
- else if (exit_reason == EXIT_REASON_PREEMPTION_TIMER)
+ else if (exit_reason.basic == EXIT_REASON_PREEMPTION_TIMER)
return handle_preemption_timer(vcpu);
- else if (exit_reason == EXIT_REASON_INTERRUPT_WINDOW)
+ else if (exit_reason.basic == EXIT_REASON_INTERRUPT_WINDOW)
return handle_interrupt_window(vcpu);
- else if (exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT)
+ else if (exit_reason.basic == EXIT_REASON_EXTERNAL_INTERRUPT)
return handle_external_interrupt(vcpu);
- else if (exit_reason == EXIT_REASON_HLT)
+ else if (exit_reason.basic == EXIT_REASON_HLT)
return kvm_emulate_halt(vcpu);
- else if (exit_reason == EXIT_REASON_EPT_MISCONFIG)
+ else if (exit_reason.basic == EXIT_REASON_EPT_MISCONFIG)
return handle_ept_misconfig(vcpu);
#endif

- exit_reason = array_index_nospec(exit_reason,
- kvm_vmx_max_exit_handlers);
- if (!kvm_vmx_exit_handlers[exit_reason])
+ exit_handler_index = array_index_nospec((u16)exit_reason.basic,
+ kvm_vmx_max_exit_handlers);
+ if (!kvm_vmx_exit_handlers[exit_handler_index])
goto unexpected_vmexit;

- return kvm_vmx_exit_handlers[exit_reason](vcpu);
+ return kvm_vmx_exit_handlers[exit_handler_index](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",
+ 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 = 2;
- vcpu->run->internal.data[0] = exit_reason;
+ vcpu->run->internal.data[0] = exit_reason.full;
vcpu->run->internal.data[1] = vcpu->arch.last_vmentry_cpu;
return 0;
}
@@ -6373,9 +6375,9 @@ static void vmx_handle_exit_irqoff(struct kvm_vcpu *vcpu)
{
struct vcpu_vmx *vmx = to_vmx(vcpu);

- if (vmx->exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT)
+ if (vmx->exit_reason.basic == EXIT_REASON_EXTERNAL_INTERRUPT)
handle_external_interrupt_irqoff(vcpu);
- else if (vmx->exit_reason == EXIT_REASON_EXCEPTION_NMI)
+ else if (vmx->exit_reason.basic == EXIT_REASON_EXCEPTION_NMI)
handle_exception_nmi_irqoff(vmx);
}

@@ -6567,7 +6569,7 @@ void noinstr vmx_update_host_rsp(struct vcpu_vmx *vmx, unsigned long host_rsp)

static fastpath_t vmx_exit_handlers_fastpath(struct kvm_vcpu *vcpu)
{
- switch (to_vmx(vcpu)->exit_reason) {
+ switch (to_vmx(vcpu)->exit_reason.basic) {
case EXIT_REASON_MSR_WRITE:
return handle_fastpath_set_msr_irqoff(vcpu);
case EXIT_REASON_PREEMPTION_TIMER:
@@ -6766,17 +6768,17 @@ static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu)
vmx->idt_vectoring_info = 0;

if (unlikely(vmx->fail)) {
- vmx->exit_reason = 0xdead;
+ vmx->exit_reason.full = 0xdead;
return EXIT_FASTPATH_NONE;
}

- vmx->exit_reason = vmcs_read32(VM_EXIT_REASON);
- if (unlikely((u16)vmx->exit_reason == EXIT_REASON_MCE_DURING_VMENTRY))
+ vmx->exit_reason.full = vmcs_read32(VM_EXIT_REASON);
+ if (unlikely(vmx->exit_reason.basic == EXIT_REASON_MCE_DURING_VMENTRY))
kvm_machine_check();

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

- if (unlikely(vmx->exit_reason & VMX_EXIT_REASONS_FAILED_VMENTRY))
+ if (unlikely(vmx->exit_reason.failed_vmentry))
return EXIT_FASTPATH_NONE;

vmx->loaded_vmcs->launched = 1;
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index 9d3a557949ac..903f246b5abd 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -70,6 +70,29 @@ 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 sgx_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.
@@ -244,7 +267,7 @@ 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;
--
2.29.2