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.dev
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

1 files changed, 15 insertions, 1 deletions

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 8170c04fde91..1201af636551 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/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);			\
 	})