KVM: arm64: Add build validation for FGT trap mask values

These checks help ensure that all the bits are accounted for,
that there hasn't been a transcribing error from the spec nor
from the generated mask values, which will be used in subsequent
patches.

Signed-off-by: Fuad Tabba <tabba@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20231214100158.2305400-12-tabba@google.com

Author: Fuad Tabba

arch/arm64/kvm/hyp/include/hyp/switch.h

@@ -79,6 +79,16 @@ static inline void __activate_traps_fpsimd32(struct kvm_vcpu *vcpu)
 		clr |= ~hfg & __ ## reg ## _nMASK; 			\
 	} while(0)
 
+/*
+ * Validate the fine grain trap masks.
+ * Check that the masks do not overlap and that all bits are accounted for.
+ */
+#define CHECK_FGT_MASKS(reg)							\
+	do {									\
+		BUILD_BUG_ON((__ ## reg ## _MASK) & (__ ## reg ## _nMASK));	\
+		BUILD_BUG_ON(~((__ ## reg ## _RES0) ^ (__ ## reg ## _MASK) ^	\
+			       (__ ## reg ## _nMASK)));				\
+	} while(0)
 
 static inline bool cpu_has_amu(void)
 {
@@ -94,6 +104,14 @@ static inline void __activate_traps_hfgxtr(struct kvm_vcpu *vcpu)
 	u64 r_clr = 0, w_clr = 0, r_set = 0, w_set = 0, tmp;
 	u64 r_val, w_val;
 
+	CHECK_FGT_MASKS(HFGRTR_EL2);
+	CHECK_FGT_MASKS(HFGWTR_EL2);
+	CHECK_FGT_MASKS(HFGITR_EL2);
+	CHECK_FGT_MASKS(HDFGRTR_EL2);
+	CHECK_FGT_MASKS(HDFGWTR_EL2);
+	CHECK_FGT_MASKS(HAFGRTR_EL2);
+	CHECK_FGT_MASKS(HCRX_EL2);
+
 	if (!cpus_have_final_cap(ARM64_HAS_FGT))
 		return;