KVM: arm64: nv: Expose up to FEAT_Debugv8p8 to NV-enabled VMs

The changes to the debug architecture up to v8.8 are concerned with
external debug, which of course has no direct impact on VMs. Raise the
feature limit and document what's preventing us from raising it further.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Marc Zyngier <maz@kernel.org>

Author: oupton

arch/arm64/kvm/nested.c

@@ -1581,8 +1581,11 @@ u64 limit_nv_id_reg(struct kvm *kvm, u32 reg, u64 val)
 			 ID_AA64DFR0_EL1_PMSS		|
 			 ID_AA64DFR0_EL1_TraceVer);
 
-		/* Cap Debug to ARMv8.1 */
-		val = ID_REG_LIMIT_FIELD_ENUM(val, ID_AA64DFR0_EL1, DebugVer, VHE);
+		/*
+		 * FEAT_Debugv8p9 requires support for extended breakpoints /
+		 * watchpoints.
+		 */
+		val = ID_REG_LIMIT_FIELD_ENUM(val, ID_AA64DFR0_EL1, DebugVer, V8P8);
 		break;
 	}