[PATCH v4 32/43] KVM: arm64: Validate FGT register descriptions against RES0 masks

[Marc Zyngier]

In order to point out to the unsuspecting KVM hacker that they
are missing something somewhere, validate that the known FGT bits
do not intersect with the corresponding RES0 mask, as computed at
boot time.

THis check is also performed at boot time, ensuring that there is
no runtime overhead.

Signed-off-by: Marc Zyngier <maz at kernel.org>
---
 arch/arm64/include/asm/kvm_host.h |  1 +
 arch/arm64/kvm/config.c           | 29 +++++++++++++++++++++++++++++
 arch/arm64/kvm/sys_regs.c         |  2 ++
 3 files changed, 32 insertions(+)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 9386f15cdc252..59bfb049ce987 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -1611,5 +1611,6 @@ void kvm_set_vm_id_reg(struct kvm *kvm, u32 reg, u64 val);
 	(kvm_has_feat((k), ID_AA64MMFR3_EL1, S1POE, IMP))
 
 void compute_fgu(struct kvm *kvm, enum fgt_group_id fgt);
+void check_feature_map(void);
 
 #endif /* __ARM64_KVM_HOST_H__ */
diff --git a/arch/arm64/kvm/config.c b/arch/arm64/kvm/config.c
index 85350b883abf7..242c82eefd5e4 100644
--- a/arch/arm64/kvm/config.c
+++ b/arch/arm64/kvm/config.c
@@ -494,6 +494,35 @@ static const struct reg_bits_to_feat_map hafgrtr_feat_map[] = {
 		   FEAT_AMUv1),
 };
 
+static void __init check_feat_map(const struct reg_bits_to_feat_map *map,
+				  int map_size, u64 res0, const char *str)
+{
+	u64 mask = 0;
+
+	for (int i = 0; i < map_size; i++)
+		mask |= map[i].bits;
+
+	if (mask != ~res0)
+		kvm_err("Undefined %s behaviour, bits %016llx\n",
+			str, mask ^ ~res0);
+}
+
+void __init check_feature_map(void)
+{
+	check_feat_map(hfgrtr_feat_map, ARRAY_SIZE(hfgrtr_feat_map),
+		       hfgrtr_masks.res0, hfgrtr_masks.str);
+	check_feat_map(hfgwtr_feat_map, ARRAY_SIZE(hfgwtr_feat_map),
+		       hfgwtr_masks.res0, hfgwtr_masks.str);
+	check_feat_map(hfgitr_feat_map, ARRAY_SIZE(hfgitr_feat_map),
+		       hfgitr_masks.res0, hfgitr_masks.str);
+	check_feat_map(hdfgrtr_feat_map, ARRAY_SIZE(hdfgrtr_feat_map),
+		       hdfgrtr_masks.res0, hdfgrtr_masks.str);
+	check_feat_map(hdfgwtr_feat_map, ARRAY_SIZE(hdfgwtr_feat_map),
+		       hdfgwtr_masks.res0, hdfgwtr_masks.str);
+	check_feat_map(hafgrtr_feat_map, ARRAY_SIZE(hafgrtr_feat_map),
+		       hafgrtr_masks.res0, hafgrtr_masks.str);
+}
+
 static bool idreg_feat_match(struct kvm *kvm, const struct reg_bits_to_feat_map *map)
 {
 	u64 regval = kvm->arch.id_regs[map->regidx];
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index b3e53a899c1fe..f24d1a7d9a8f4 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -5208,6 +5208,8 @@ int __init kvm_sys_reg_table_init(void)
 
 	ret = populate_nv_trap_config();
 
+	check_feature_map();
+
 	for (i = 0; !ret && i < ARRAY_SIZE(sys_reg_descs); i++)
 		ret = populate_sysreg_config(sys_reg_descs + i, i);
 
-- 
2.39.2