KVM: arm64: nv: Add kvm_has_pauth() helper

Pointer Authentication comes in many flavors, and a faithful emulation
relies on correctly handling the flavour implemented by the HW.

For this, provide a new kvm_has_pauth() that checks whether we
expose to the guest a particular level of support. This checks
across all 3 possible authentication algorithms (Q5, Q3 and IMPDEF).
Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20240419102935.1935571-12-maz@kernel.orgSigned-off-by: Marc Zyngier <maz@kernel.org>

arch/arm64/include/asm/kvm_host.h

@@ -1336,4 +1336,19 @@ bool kvm_arm_vcpu_stopped(struct kvm_vcpu *vcpu);
 	(get_idreg_field((kvm), id, fld) >= expand_field_sign(id, fld, min) && \
 	 get_idreg_field((kvm), id, fld) <= expand_field_sign(id, fld, max))
 
+/* Check for a given level of PAuth support */
+#define kvm_has_pauth(k, l)						\
+	({								\
+		bool pa, pi, pa3;					\
+									\
+		pa  = kvm_has_feat((k), ID_AA64ISAR1_EL1, APA, l);	\
+		pa &= kvm_has_feat((k), ID_AA64ISAR1_EL1, GPA, IMP);	\
+		pi  = kvm_has_feat((k), ID_AA64ISAR1_EL1, API, l);	\
+		pi &= kvm_has_feat((k), ID_AA64ISAR1_EL1, GPI, IMP);	\
+		pa3  = kvm_has_feat((k), ID_AA64ISAR2_EL1, APA3, l);	\
+		pa3 &= kvm_has_feat((k), ID_AA64ISAR2_EL1, GPA3, IMP);	\
+									\
+		(pa + pi + pa3) == 1;					\
+	})
+
 #endif /* __ARM64_KVM_HOST_H__ */