KVM: arm64: Use read-only helper for reading VM ID registers

IDREG() expands to the storage of a particular ID reg, which can be
useful for handling both reads and writes. However, outside of a select
few situations, the ID registers should be considered read only.

Replace current readers with a new macro that expands to the value of
the field rather than the field itself.
Reviewed-by: Sebastian Ott <sebott@redhat.com>
Link: https://lore.kernel.org/r/20240619174036.483943-4-oliver.upton@linux.devSigned-off-by: Oliver Upton <oliver.upton@linux.dev>

arch/arm64/include/asm/kvm_host.h

@@ -1332,6 +1332,20 @@ static inline void kvm_hyp_reserve(void) { }
 void kvm_arm_vcpu_power_off(struct kvm_vcpu *vcpu);
 bool kvm_arm_vcpu_stopped(struct kvm_vcpu *vcpu);
 
+static inline u64 *__vm_id_reg(struct kvm_arch *ka, u32 reg)
+{
+	switch (reg) {
+	case sys_reg(3, 0, 0, 1, 0) ... sys_reg(3, 0, 0, 7, 7):
+		return &ka->id_regs[IDREG_IDX(reg)];
+	default:
+		WARN_ON_ONCE(1);
+		return NULL;
+	}
+}
+
+#define kvm_read_vm_id_reg(kvm, reg)					\
+	({ u64 __val = *__vm_id_reg(&(kvm)->arch, reg); __val; })
+
 #define __expand_field_sign_unsigned(id, fld, val)			\
 	((u64)SYS_FIELD_VALUE(id, fld, val))
 
@@ -1348,7 +1362,7 @@ bool kvm_arm_vcpu_stopped(struct kvm_vcpu *vcpu);
 
 #define get_idreg_field_unsigned(kvm, id, fld)				\
 	({								\
-		u64 __val = IDREG((kvm), SYS_##id);			\
+		u64 __val = kvm_read_vm_id_reg((kvm), SYS_##id);	\
 		FIELD_GET(id##_##fld##_MASK, __val);			\
 	})
 

arch/arm64/kvm/pmu-emul.c

@@ -54,7 +54,7 @@ static u32 __kvm_pmu_event_mask(unsigned int pmuver)
 
 static u32 kvm_pmu_event_mask(struct kvm *kvm)
 {
-	u64 dfr0 = IDREG(kvm, SYS_ID_AA64DFR0_EL1);
+	u64 dfr0 = kvm_read_vm_id_reg(kvm, SYS_ID_AA64DFR0_EL1);
 	u8 pmuver = SYS_FIELD_GET(ID_AA64DFR0_EL1, PMUVer, dfr0);
 
 	return __kvm_pmu_event_mask(pmuver);

arch/arm64/kvm/sys_regs.c

@@ -1565,7 +1565,7 @@ static u64 kvm_read_sanitised_id_reg(struct kvm_vcpu *vcpu,
 
 static u64 read_id_reg(const struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
 {
-	return IDREG(vcpu->kvm, reg_to_encoding(r));
+	return kvm_read_vm_id_reg(vcpu->kvm, reg_to_encoding(r));
 }
 
 static bool is_feature_id_reg(u32 encoding)
@@ -2760,7 +2760,7 @@ static bool trap_dbgdidr(struct kvm_vcpu *vcpu,
 	if (p->is_write) {
 		return ignore_write(vcpu, p);
 	} else {
-		u64 dfr = IDREG(vcpu->kvm, SYS_ID_AA64DFR0_EL1);
+		u64 dfr = kvm_read_vm_id_reg(vcpu->kvm, SYS_ID_AA64DFR0_EL1);
 		u32 el3 = kvm_has_feat(vcpu->kvm, ID_AA64PFR0_EL1, EL3, IMP);
 
 		p->regval = ((SYS_FIELD_GET(ID_AA64DFR0_EL1, WRPs, dfr) << 28) |
@@ -3519,7 +3519,7 @@ static int idregs_debug_show(struct seq_file *s, void *v)
 		return 0;
 
 	seq_printf(s, "%20s:\t%016llx\n",
-		   desc->name, IDREG(kvm, reg_to_encoding(desc)));
+		   desc->name, kvm_read_vm_id_reg(kvm, reg_to_encoding(desc)));
 
 	return 0;
 }