KVM: x86: Consolidate guest enter/exit logic to common helpers

Move the enter/exit logic in {svm,vmx}_vcpu_enter_exit() to common
helpers.  Opportunistically update the somewhat stale comment about the
updates needing to occur immediately after VM-Exit.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20210505002735.1684165-9-seanjc@google.com

Author: sean-jc

arch/x86/kvm/svm/svm.c

@@ -3710,25 +3710,7 @@ static noinstr void svm_vcpu_enter_exit(struct kvm_vcpu *vcpu)
 	struct vcpu_svm *svm = to_svm(vcpu);
 	unsigned long vmcb_pa = svm->current_vmcb->pa;
 
-	/*
-	 * VMENTER enables interrupts (host state), but the kernel state is
-	 * interrupts disabled when this is invoked. Also tell RCU about
-	 * it. This is the same logic as for exit_to_user_mode().
-	 *
-	 * This ensures that e.g. latency analysis on the host observes
-	 * guest mode as interrupt enabled.
-	 *
-	 * guest_enter_irqoff() informs context tracking about the
-	 * transition to guest mode and if enabled adjusts RCU state
-	 * accordingly.
-	 */
-	instrumentation_begin();
-	trace_hardirqs_on_prepare();
-	lockdep_hardirqs_on_prepare(CALLER_ADDR0);
-	instrumentation_end();
-
-	guest_enter_irqoff();
-	lockdep_hardirqs_on(CALLER_ADDR0);
+	kvm_guest_enter_irqoff();
 
 	if (sev_es_guest(vcpu->kvm)) {
 		__svm_sev_es_vcpu_run(vmcb_pa);
@@ -3748,24 +3730,7 @@ static noinstr void svm_vcpu_enter_exit(struct kvm_vcpu *vcpu)
 		vmload(__sme_page_pa(sd->save_area));
 	}
 
-	/*
-	 * VMEXIT disables interrupts (host state), but tracing and lockdep
-	 * have them in state 'on' as recorded before entering guest mode.
-	 * Same as enter_from_user_mode().
-	 *
-	 * context_tracking_guest_exit() restores host context and reinstates
-	 * RCU if enabled and required.
-	 *
-	 * This needs to be done before the below as native_read_msr()
-	 * contains a tracepoint and x86_spec_ctrl_restore_host() calls
-	 * into world and some more.
-	 */
-	lockdep_hardirqs_off(CALLER_ADDR0);
-	context_tracking_guest_exit();
-
-	instrumentation_begin();
-	trace_hardirqs_off_finish();
-	instrumentation_end();
+	kvm_guest_exit_irqoff();
 }
 
 static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu)

arch/x86/kvm/vmx/vmx.c

@@ -6664,25 +6664,7 @@ static fastpath_t vmx_exit_handlers_fastpath(struct kvm_vcpu *vcpu)
 static noinstr void vmx_vcpu_enter_exit(struct kvm_vcpu *vcpu,
 					struct vcpu_vmx *vmx)
 {
-	/*
-	 * VMENTER enables interrupts (host state), but the kernel state is
-	 * interrupts disabled when this is invoked. Also tell RCU about
-	 * it. This is the same logic as for exit_to_user_mode().
-	 *
-	 * This ensures that e.g. latency analysis on the host observes
-	 * guest mode as interrupt enabled.
-	 *
-	 * guest_enter_irqoff() informs context tracking about the
-	 * transition to guest mode and if enabled adjusts RCU state
-	 * accordingly.
-	 */
-	instrumentation_begin();
-	trace_hardirqs_on_prepare();
-	lockdep_hardirqs_on_prepare(CALLER_ADDR0);
-	instrumentation_end();
-
-	guest_enter_irqoff();
-	lockdep_hardirqs_on(CALLER_ADDR0);
+	kvm_guest_enter_irqoff();
 
 	/* L1D Flush includes CPU buffer clear to mitigate MDS */
 	if (static_branch_unlikely(&vmx_l1d_should_flush))
@@ -6698,24 +6680,7 @@ static noinstr void vmx_vcpu_enter_exit(struct kvm_vcpu *vcpu,
 
 	vcpu->arch.cr2 = native_read_cr2();
 
-	/*
-	 * VMEXIT disables interrupts (host state), but tracing and lockdep
-	 * have them in state 'on' as recorded before entering guest mode.
-	 * Same as enter_from_user_mode().
-	 *
-	 * context_tracking_guest_exit() restores host context and reinstates
-	 * RCU if enabled and required.
-	 *
-	 * This needs to be done before the below as native_read_msr()
-	 * contains a tracepoint and x86_spec_ctrl_restore_host() calls
-	 * into world and some more.
-	 */
-	lockdep_hardirqs_off(CALLER_ADDR0);
-	context_tracking_guest_exit();
-
-	instrumentation_begin();
-	trace_hardirqs_off_finish();
-	instrumentation_end();
+	kvm_guest_exit_irqoff();
 }
 
 static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu)

arch/x86/kvm/x86.h

@@ -8,6 +8,51 @@
 #include "kvm_cache_regs.h"
 #include "kvm_emulate.h"
 
+static __always_inline void kvm_guest_enter_irqoff(void)
+{
+	/*
+	 * VMENTER enables interrupts (host state), but the kernel state is
+	 * interrupts disabled when this is invoked. Also tell RCU about
+	 * it. This is the same logic as for exit_to_user_mode().
+	 *
+	 * This ensures that e.g. latency analysis on the host observes
+	 * guest mode as interrupt enabled.
+	 *
+	 * guest_enter_irqoff() informs context tracking about the
+	 * transition to guest mode and if enabled adjusts RCU state
+	 * accordingly.
+	 */
+	instrumentation_begin();
+	trace_hardirqs_on_prepare();
+	lockdep_hardirqs_on_prepare(CALLER_ADDR0);
+	instrumentation_end();
+
+	guest_enter_irqoff();
+	lockdep_hardirqs_on(CALLER_ADDR0);
+}
+
+static __always_inline void kvm_guest_exit_irqoff(void)
+{
+	/*
+	 * VMEXIT disables interrupts (host state), but tracing and lockdep
+	 * have them in state 'on' as recorded before entering guest mode.
+	 * Same as enter_from_user_mode().
+	 *
+	 * context_tracking_guest_exit() restores host context and reinstates
+	 * RCU if enabled and required.
+	 *
+	 * This needs to be done immediately after VM-Exit, before any code
+	 * that might contain tracepoints or call out to the greater world,
+	 * e.g. before x86_spec_ctrl_restore_host().
+	 */
+	lockdep_hardirqs_off(CALLER_ADDR0);
+	context_tracking_guest_exit();
+
+	instrumentation_begin();
+	trace_hardirqs_off_finish();
+	instrumentation_end();
+}
+
 #define KVM_NESTED_VMENTER_CONSISTENCY_CHECK(consistency_check)		\
 ({									\
 	bool failed = (consistency_check);				\