KVM: arm64: Compute MDCR_EL2 at vcpu_load()

KVM has picked up several hacks to cope with vcpu->arch.mdcr_el2 needing
to be prepared before vcpu_load(), which is when it gets programmed
into hardware on VHE.

Now that the flows for reprogramming MDCR_EL2 have been simplified, move
that computation to vcpu_load().

Tested-by: James Clark <james.clark@linaro.org>
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20241219224116.3941496-14-oliver.upton@linux.dev
Signed-off-by: Marc Zyngier <maz@kernel.org>

Author: oupton

arch/arm64/include/asm/kvm_host.h

@@ -1341,7 +1341,6 @@ static inline bool kvm_system_needs_idmapped_vectors(void)
 static inline void kvm_arch_sync_events(struct kvm *kvm) {}
 
 void kvm_init_host_debug_data(void);
-void kvm_arm_vcpu_init_debug(struct kvm_vcpu *vcpu);
 void kvm_arm_setup_debug(struct kvm_vcpu *vcpu);
 void kvm_arm_clear_debug(struct kvm_vcpu *vcpu);
 void kvm_vcpu_load_debug(struct kvm_vcpu *vcpu);

arch/arm64/kvm/arm.c

@@ -804,8 +804,6 @@ int kvm_arch_vcpu_run_pid_change(struct kvm_vcpu *vcpu)
 
 	kvm_init_mpidr_data(kvm);
 
-	kvm_arm_vcpu_init_debug(vcpu);
-
 	if (likely(irqchip_in_kernel(kvm))) {
 		/*
 		 * Map the VGIC hardware resources before running a vcpu the

arch/arm64/kvm/debug.c

@@ -98,20 +98,6 @@ static void kvm_arm_setup_mdcr_el2(struct kvm_vcpu *vcpu)
 	preempt_enable();
 }
 
-/**
- * kvm_arm_vcpu_init_debug - setup vcpu debug traps
- *
- * @vcpu:	the vcpu pointer
- *
- * Set vcpu initial mdcr_el2 value.
- */
-void kvm_arm_vcpu_init_debug(struct kvm_vcpu *vcpu)
-{
-	preempt_disable();
-	kvm_arm_setup_mdcr_el2(vcpu);
-	preempt_enable();
-}
-
 /**
  * kvm_arm_setup_debug - set up debug related stuff
  *
@@ -131,8 +117,6 @@ void kvm_arm_setup_debug(struct kvm_vcpu *vcpu)
 {
 	unsigned long mdscr;
 
-	kvm_arm_setup_mdcr_el2(vcpu);
-
 	/* Check if we need to use the debug registers. */
 	if (vcpu->guest_debug || kvm_vcpu_os_lock_enabled(vcpu)) {
 		/* Save guest debug state */
@@ -273,6 +257,8 @@ void kvm_vcpu_load_debug(struct kvm_vcpu *vcpu)
 		else
 			vcpu->arch.debug_owner = VCPU_DEBUG_FREE;
 	}
+
+	kvm_arm_setup_mdcr_el2(vcpu);
 }
 
 /*
@@ -287,6 +273,7 @@ void kvm_debug_set_guest_ownership(struct kvm_vcpu *vcpu)
 		return;
 
 	vcpu->arch.debug_owner = VCPU_DEBUG_GUEST_OWNED;
+	kvm_arm_setup_mdcr_el2(vcpu);
 }
 
 void kvm_debug_handle_oslar(struct kvm_vcpu *vcpu, u64 val)