KVM: arm64: Make vcpu const in vcpu_read_sys_reg

vcpu_read_sys_reg should not be modifying the VCPU structure.
Eventually, to handle EL2 sysregs for nested virtualization, we will
call vcpu_read_sys_reg from places that have a const vcpu pointer, which
will complain about the lack of the const modifier on the read path.

Signed-off-by: Christoffer Dall <christoffer.dall@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 7a5035f..c22e50b 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -319,7 +319,7 @@ struct kvm_vcpu_arch {
  */
 #define __vcpu_sys_reg(v,r)	((v)->arch.ctxt.sys_regs[(r)])
 
-u64 vcpu_read_sys_reg(struct kvm_vcpu *vcpu, int reg);
+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);
 
 /*
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index ecbf67c..965c6f1 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -76,7 +76,7 @@ static bool write_to_read_only(struct kvm_vcpu *vcpu,
 	return false;
 }
 
-u64 vcpu_read_sys_reg(struct kvm_vcpu *vcpu, int reg)
+u64 vcpu_read_sys_reg(const struct kvm_vcpu *vcpu, int reg)
 {
 	if (!vcpu->arch.sysregs_loaded_on_cpu)
 		goto immediate_read;