Merge branch kvm-arm64/nv-debug into kvmarm-master/next

* kvm-arm64/nv-debug:
  : .
  : Fix handling of MDSCR_EL1 in NV context, which is unfortunately
  : mishandled by the architecture. Patches courtesy of Oliver Upton
  : (20250917203125.283116-2-oliver.upton@linux.dev)
  : .
  KVM: arm64: nv: Apply guest's MDCR traps in nested context
  KVM: arm64: nv: Trap debug registers when in hyp context

Signed-off-by: Marc Zyngier <maz@kernel.org>

Author: Marc Zyngier

arch/arm64/include/asm/kvm_nested.h

@@ -83,6 +83,8 @@ extern void check_nested_vcpu_requests(struct kvm_vcpu *vcpu);
 extern void kvm_nested_flush_hwstate(struct kvm_vcpu *vcpu);
 extern void kvm_nested_sync_hwstate(struct kvm_vcpu *vcpu);
 
+extern void kvm_nested_setup_mdcr_el2(struct kvm_vcpu *vcpu);
+
 struct kvm_s2_trans {
 	phys_addr_t output;
 	unsigned long block_size;

arch/arm64/kvm/debug.c

@@ -56,6 +56,9 @@ static void kvm_arm_setup_mdcr_el2(struct kvm_vcpu *vcpu)
 	if (!kvm_guest_owns_debug_regs(vcpu))
 		vcpu->arch.mdcr_el2 |= MDCR_EL2_TDA;
 
+	if (vcpu_has_nv(vcpu))
+		kvm_nested_setup_mdcr_el2(vcpu);
+
 	/* Write MDCR_EL2 directly if we're already at EL2 */
 	if (has_vhe())
 		write_sysreg(vcpu->arch.mdcr_el2, mdcr_el2);

arch/arm64/kvm/nested.c

@@ -1796,3 +1796,33 @@ void kvm_nested_sync_hwstate(struct kvm_vcpu *vcpu)
 	if (unlikely(vcpu_test_and_clear_flag(vcpu, NESTED_SERROR_PENDING)))
 		kvm_inject_serror_esr(vcpu, vcpu_get_vsesr(vcpu));
 }
+
+/*
+ * KVM unconditionally sets most of these traps anyway but use an allowlist
+ * to document the guest hypervisor traps that may take precedence and guard
+ * against future changes to the non-nested trap configuration.
+ */
+#define NV_MDCR_GUEST_INCLUDE	(MDCR_EL2_TDE	|	\
+				 MDCR_EL2_TDA	|	\
+				 MDCR_EL2_TDRA	|	\
+				 MDCR_EL2_TTRF	|	\
+				 MDCR_EL2_TPMS	|	\
+				 MDCR_EL2_TPM	|	\
+				 MDCR_EL2_TPMCR	|	\
+				 MDCR_EL2_TDCC	|	\
+				 MDCR_EL2_TDOSA)
+
+void kvm_nested_setup_mdcr_el2(struct kvm_vcpu *vcpu)
+{
+	u64 guest_mdcr = __vcpu_sys_reg(vcpu, MDCR_EL2);
+
+	/*
+	 * In yet another example where FEAT_NV2 is fscking broken, accesses
+	 * to MDSCR_EL1 are redirected to the VNCR despite having an effect
+	 * at EL2. Use a big hammer to apply sanity.
+	 */
+	if (is_hyp_ctxt(vcpu))
+		vcpu->arch.mdcr_el2 |= MDCR_EL2_TDA;
+	else
+		vcpu->arch.mdcr_el2 |= (guest_mdcr & NV_MDCR_GUEST_INCLUDE);
+}