[PATCH v3 0/2] KVM: VMX: Unionize vcpu_vmx.exit_reason

[PATCH v3 0/2] KVM: VMX: Unionize vcpu_vmx.exit_reason

[Sean Christopherson]

Minor fixup patch for a mishandled conflict between the vmcs.INTR_INFO
caching series and the union series, plus the actual unionization patch
rebased onto kvm/queue, commit 604e8bba0dc5 ("KVM: Remove redundant ...").

Sean Christopherson (2):
  KVM: nVMX: Drop a redundant call to vmx_get_intr_info()
  KVM: VMX: Convert vcpu_vmx.exit_reason to a union

 arch/x86/kvm/vmx/nested.c | 39 ++++++++++++++---------
 arch/x86/kvm/vmx/vmx.c    | 65 ++++++++++++++++++++-------------------
 arch/x86/kvm/vmx/vmx.h    | 25 ++++++++++++++-
 3 files changed, 83 insertions(+), 46 deletions(-)

-- 
2.26.0

[PATCH v3 1/2] KVM: nVMX: Drop a redundant call to vmx_get_intr_info()

[Sean Christopherson]

Drop nested_vmx_l1_wants_exit()'s initialization of intr_info from
vmx_get_intr_info() that was inadvertantly introduced along with the
caching mechanism.  EXIT_REASON_EXCEPTION_NMI, the only consumer of
intr_info, populates the variable before using it.

Fixes: bb53120d67cdb ("KVM: VMX: Cache vmcs.EXIT_INTR_INFO using arch avail_reg flags")
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
 arch/x86/kvm/vmx/nested.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index f228339cd0a0..995c319cc7ad 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -5691,8 +5691,8 @@ static bool nested_vmx_l0_wants_exit(struct kvm_vcpu *vcpu, u32 exit_reason)
  */
 static bool nested_vmx_l1_wants_exit(struct kvm_vcpu *vcpu, u32 exit_reason)
 {
-	u32 intr_info = vmx_get_intr_info(vcpu);
 	struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
+	u32 intr_info;
 
 	switch (exit_reason) {
 	case EXIT_REASON_EXCEPTION_NMI:
-- 
2.26.0

[PATCH v3 2/2] KVM: VMX: Convert vcpu_vmx.exit_reason to a union

[Sean Christopherson]

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.

Cc: Xiaoyao Li <xiaoyao.li@intel.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
 arch/x86/kvm/vmx/nested.c | 37 ++++++++++++++--------
 arch/x86/kvm/vmx/vmx.c    | 65 ++++++++++++++++++++-------------------
 arch/x86/kvm/vmx/vmx.h    | 25 ++++++++++++++-
 3 files changed, 82 insertions(+), 45 deletions(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 995c319cc7ad..dd41735dc1b0 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -3247,7 +3247,10 @@ enum nvmx_vmentry_status nested_vmx_enter_non_root_mode(struct kvm_vcpu *vcpu,
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 	struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
 	bool evaluate_pending_interrupts;
-	u32 exit_reason = EXIT_REASON_INVALID_STATE;
+	union vmx_exit_reason exit_reason = {
+		.basic = EXIT_REASON_INVALID_STATE,
+		.failed_vmentry = 1,
+	};
 	u32 exit_qual;
 
 	if (kvm_check_request(KVM_REQ_TLB_FLUSH_CURRENT, vcpu))
@@ -3308,7 +3311,7 @@ enum nvmx_vmentry_status nested_vmx_enter_non_root_mode(struct kvm_vcpu *vcpu,
 		goto vmentry_fail_vmexit_guest_mode;
 
 	if (from_vmentry) {
-		exit_reason = EXIT_REASON_MSR_LOAD_FAIL;
+		exit_reason.basic = EXIT_REASON_MSR_LOAD_FAIL;
 		exit_qual = nested_vmx_load_msr(vcpu,
 						vmcs12->vm_entry_msr_load_addr,
 						vmcs12->vm_entry_msr_load_count);
@@ -3376,7 +3379,7 @@ 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;
 	vmcs12->exit_qualification = exit_qual;
 	if (enable_shadow_vmcs || vmx->nested.hv_evmcs)
 		vmx->nested.need_vmcs12_to_shadow_sync = true;
@@ -5410,7 +5413,12 @@ 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;
@@ -5478,7 +5486,8 @@ 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;
@@ -5492,7 +5501,7 @@ 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;
@@ -5629,11 +5638,12 @@ 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 (exit_reason) {
+	switch (exit_reason.basic) {
 	case EXIT_REASON_EXCEPTION_NMI:
 		intr_info = vmx_get_intr_info(vcpu);
 		if (is_nmi(intr_info))
@@ -5689,12 +5699,13 @@ 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 (exit_reason) {
+	switch (exit_reason.basic) {
 	case EXIT_REASON_EXCEPTION_NMI:
 		intr_info = vmx_get_intr_info(vcpu);
 		if (is_nmi(intr_info))
@@ -5813,7 +5824,7 @@ 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;
 	u32 exit_intr_info, exit_qual;
 
 	WARN_ON_ONCE(vmx->nested.nested_run_pending);
@@ -5834,7 +5845,7 @@ bool nested_vmx_reflect_vmexit(struct kvm_vcpu *vcpu)
 	exit_intr_info = vmx_get_intr_info(vcpu);
 	exit_qual = vmx_get_exit_qual(vcpu);
 
-	trace_kvm_nested_vmexit(kvm_rip_read(vcpu), exit_reason, exit_qual,
+	trace_kvm_nested_vmexit(kvm_rip_read(vcpu), exit_reason.full, exit_qual,
 				vmx->idt_vectoring_info, exit_intr_info,
 				vmcs_read32(VM_EXIT_INTR_ERROR_CODE),
 				KVM_ISA_VMX);
@@ -5863,7 +5874,7 @@ bool nested_vmx_reflect_vmexit(struct kvm_vcpu *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 766303b31949..28035c77a03c 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1567,7 +1567,7 @@ 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);
@@ -5869,10 +5869,11 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu,
 	enum exit_fastpath_completion 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;
 
-	trace_kvm_exit(exit_reason, vcpu, KVM_ISA_VMX);
+	trace_kvm_exit(exit_reason.full, vcpu, KVM_ISA_VMX);
 
 	/*
 	 * Flush logged GPAs PML buffer, this will make dirty_bitmap more
@@ -5906,11 +5907,11 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu,
 			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;
 		return 0;
 	}
 
@@ -5930,17 +5931,17 @@ 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)) {
+	    (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_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);
@@ -5972,38 +5973,39 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu,
 		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 = 1;
-	vcpu->run->internal.data[0] = exit_reason;
+	vcpu->run->internal.data[0] = exit_reason.full;
 	return 0;
 }
 
@@ -6354,9 +6356,9 @@ 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);
 }
 
@@ -6722,18 +6724,19 @@ static enum exit_fastpath_completion 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();
 
-	if (unlikely(vmx->exit_reason & VMX_EXIT_REASONS_FAILED_VMENTRY))
+	if (unlikely(vmx->exit_reason.failed_vmentry))
 		return EXIT_FASTPATH_NONE;
 
-	if (!is_guest_mode(vcpu) && vmx->exit_reason == EXIT_REASON_MSR_WRITE)
+	if (!is_guest_mode(vcpu) &&
+	    vmx->exit_reason.basic == EXIT_REASON_MSR_WRITE)
 		exit_fastpath = handle_fastpath_set_msr_irqoff(vcpu);
 	else
 		exit_fastpath = EXIT_FASTPATH_NONE;
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index edfb739e5907..ef1539cdb416 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -91,6 +91,29 @@ 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;
-- 
2.26.0

Re: [PATCH v3 0/2] KVM: VMX: Unionize vcpu_vmx.exit_reason

[Paolo Bonzini]

On 21/04/20 09:53, Sean Christopherson wrote:
> Minor fixup patch for a mishandled conflict between the vmcs.INTR_INFO
> caching series and the union series, plus the actual unionization patch
> rebased onto kvm/queue, commit 604e8bba0dc5 ("KVM: Remove redundant ...").
> 
> Sean Christopherson (2):
>   KVM: nVMX: Drop a redundant call to vmx_get_intr_info()
>   KVM: VMX: Convert vcpu_vmx.exit_reason to a union
> 
>  arch/x86/kvm/vmx/nested.c | 39 ++++++++++++++---------
>  arch/x86/kvm/vmx/vmx.c    | 65 ++++++++++++++++++++-------------------
>  arch/x86/kvm/vmx/vmx.h    | 25 ++++++++++++++-
>  3 files changed, 83 insertions(+), 46 deletions(-)
> 

Thanks, I queued patch 1.  I am not too enthusiastic about patch 2, but
when SGX comes around it may be a better idea.

Paolo

Re: [PATCH v3 0/2] KVM: VMX: Unionize vcpu_vmx.exit_reason

[Sean Christopherson]

On Tue, Apr 21, 2020 at 06:19:15PM +0200, Paolo Bonzini wrote:
> On 21/04/20 09:53, Sean Christopherson wrote:
> > Minor fixup patch for a mishandled conflict between the vmcs.INTR_INFO
> > caching series and the union series, plus the actual unionization patch
> > rebased onto kvm/queue, commit 604e8bba0dc5 ("KVM: Remove redundant ...").
> > 
> > Sean Christopherson (2):
> >   KVM: nVMX: Drop a redundant call to vmx_get_intr_info()
> >   KVM: VMX: Convert vcpu_vmx.exit_reason to a union
> > 
> >  arch/x86/kvm/vmx/nested.c | 39 ++++++++++++++---------
> >  arch/x86/kvm/vmx/vmx.c    | 65 ++++++++++++++++++++-------------------
> >  arch/x86/kvm/vmx/vmx.h    | 25 ++++++++++++++-
> >  3 files changed, 83 insertions(+), 46 deletions(-)
> > 
> 
> Thanks, I queued patch 1.  I am not too enthusiastic about patch 2, but
> when SGX comes around it may be a better idea.

And maybe it'll grow on you by the time I figure out how to send a pull
request ;-).