KVM: arm64: nv: Honor MDCR_EL2.TDE routing for debug exceptions

Inject debug exceptions into vEL2 if MDCR_EL2.TDE is set.

Tested-by: James Clark <james.clark@linaro.org>
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20241219224116.3941496-17-oliver.upton@linux.dev
Signed-off-by: Marc Zyngier <maz@kernel.org>

arch/arm64/include/asm/kvm_nested.h

@@ -64,6 +64,7 @@ static inline u64 translate_ttbr0_el2_to_ttbr0_el1(u64 ttbr0)
 }
 
 extern bool forward_smc_trap(struct kvm_vcpu *vcpu);
+extern bool forward_debug_exception(struct kvm_vcpu *vcpu);
 extern void kvm_init_nested(struct kvm *kvm);
 extern int kvm_vcpu_init_nested(struct kvm_vcpu *vcpu);
 extern void kvm_init_nested_s2_mmu(struct kvm_s2_mmu *mmu);

arch/arm64/kvm/emulate-nested.c

@@ -2345,24 +2345,39 @@ bool triage_sysreg_trap(struct kvm_vcpu *vcpu, int *sr_index)
 	return true;
 }
 
-static bool forward_traps(struct kvm_vcpu *vcpu, u64 control_bit)
+static bool __forward_traps(struct kvm_vcpu *vcpu, unsigned int reg, u64 control_bit)
 {
 	bool control_bit_set;
 
 	if (!vcpu_has_nv(vcpu))
 		return false;
 
-	control_bit_set = __vcpu_sys_reg(vcpu, HCR_EL2) & control_bit;
+	control_bit_set = __vcpu_sys_reg(vcpu, reg) & control_bit;
 	if (!is_hyp_ctxt(vcpu) && control_bit_set) {
 		kvm_inject_nested_sync(vcpu, kvm_vcpu_get_esr(vcpu));
 		return true;
 	}
 	return false;
 }
 
+static bool forward_hcr_traps(struct kvm_vcpu *vcpu, u64 control_bit)
+{
+	return __forward_traps(vcpu, HCR_EL2, control_bit);
+}
+
 bool forward_smc_trap(struct kvm_vcpu *vcpu)
 {
-	return forward_traps(vcpu, HCR_TSC);
+	return forward_hcr_traps(vcpu, HCR_TSC);
+}
+
+static bool forward_mdcr_traps(struct kvm_vcpu *vcpu, u64 control_bit)
+{
+	return __forward_traps(vcpu, MDCR_EL2, control_bit);
+}
+
+bool forward_debug_exception(struct kvm_vcpu *vcpu)
+{
+	return forward_mdcr_traps(vcpu, MDCR_EL2_TDE);
 }
 
 static u64 kvm_check_illegal_exception_return(struct kvm_vcpu *vcpu, u64 spsr)
@@ -2406,7 +2421,7 @@ void kvm_emulate_nested_eret(struct kvm_vcpu *vcpu)
 	 * Forward this trap to the virtual EL2 if the virtual
 	 * HCR_EL2.NV bit is set and this is coming from !EL2.
 	 */
-	if (forward_traps(vcpu, HCR_NV))
+	if (forward_hcr_traps(vcpu, HCR_NV))
 		return;
 
 	spsr = vcpu_read_sys_reg(vcpu, SPSR_EL2);

arch/arm64/kvm/handle_exit.c

@@ -183,6 +183,9 @@ static int kvm_handle_guest_debug(struct kvm_vcpu *vcpu)
 	struct kvm_run *run = vcpu->run;
 	u64 esr = kvm_vcpu_get_esr(vcpu);
 
+	if (!vcpu->guest_debug && forward_debug_exception(vcpu))
+		return 1;
+
 	run->exit_reason = KVM_EXIT_DEBUG;
 	run->debug.arch.hsr = lower_32_bits(esr);
 	run->debug.arch.hsr_high = upper_32_bits(esr);