KVM: arm64: Introduce accessor for ctxt->sys_reg

In order to allow the disintegration of the per-vcpu sysreg array,
let's introduce a new helper (ctxt_sys_reg()) that returns the
in-memory copy of a system register, picked from a given context.

__vcpu_sys_reg() is rewritten to use this helper.
Signed-off-by: Marc Zyngier <maz@kernel.org>

arch/arm64/include/asm/kvm_host.h

@@ -405,12 +405,17 @@ struct kvm_vcpu_arch {
 #define vcpu_gp_regs(v)		(&(v)->arch.ctxt.gp_regs)
 
 /*
- * Only use __vcpu_sys_reg if you know you want the memory backed version of a
- * register, and not the one most recently accessed by a running VCPU.  For
- * example, for userspace access or for system registers that are never context
- * switched, but only emulated.
+ * Only use __vcpu_sys_reg/ctxt_sys_reg if you know you want the
+ * memory backed version of a register, and not the one most recently
+ * accessed by a running VCPU.  For example, for userspace access or
+ * for system registers that are never context switched, but only
+ * emulated.
  */
-#define __vcpu_sys_reg(v,r)	((v)->arch.ctxt.sys_regs[(r)])
+#define __ctxt_sys_reg(c,r)	(&(c)->sys_regs[(r)])
+
+#define ctxt_sys_reg(c,r)	(*__ctxt_sys_reg(c,r))
+
+#define __vcpu_sys_reg(v,r)	(ctxt_sys_reg(&(v)->arch.ctxt, (r)))
 
 u64 vcpu_read_sys_reg(const struct kvm_vcpu *vcpu, int reg);
 void vcpu_write_sys_reg(struct kvm_vcpu *vcpu, u64 val, int reg);