KVM: arm64: Add timer UAPI workaround to sysreg infrastructure

Amongst the numerous bugs that plague the KVM/arm64 UAPI, one of
the most annoying thing is that the userspace view of the virtual
timer has its CVAL and CNT encodings swapped.

In order to reduce the amount of code that has to know about this,
start by adding handling for this bug in the sys_reg code.

Nothing is making use of it yet, as the code responsible for userspace
interaction is catching the accesses early.

Signed-off-by: Marc Zyngier <[e-mail]>

arch/arm64/kvm/sys_regs.c

···
 	}
 }
 
+static u64 kvm_one_reg_to_id(const struct kvm_one_reg *reg)
+{
+	switch(reg->id) {
+	case KVM_REG_ARM_TIMER_CVAL:
+		return TO_ARM64_SYS_REG(CNTV_CVAL_EL0);
+	case KVM_REG_ARM_TIMER_CNT:
+		return TO_ARM64_SYS_REG(CNTVCT_EL0);
+	default:
+		return reg->id;
+	}
+}
+
 int kvm_sys_reg_get_user(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg,
 			 const struct sys_reg_desc table[], unsigned int num)
 {
 	u64 __user *uaddr = (u64 __user *)(unsigned long)reg->addr;
 	const struct sys_reg_desc *r;
+	u64 id = kvm_one_reg_to_id(reg);
 	u64 val;
 	int ret;
 
-	r = id_to_sys_reg_desc(vcpu, reg->id, table, num);
+	r = id_to_sys_reg_desc(vcpu, id, table, num);
 	if (!r || sysreg_hidden(vcpu, r))
 		return -ENOENT;
 
···
 {
 	u64 __user *uaddr = (u64 __user *)(unsigned long)reg->addr;
 	const struct sys_reg_desc *r;
+	u64 id = kvm_one_reg_to_id(reg);
 	u64 val;
 	int ret;
 
 	if (get_user(val, uaddr))
 		return -EFAULT;
 
-	r = id_to_sys_reg_desc(vcpu, reg->id, table, num);
+	r = id_to_sys_reg_desc(vcpu, id, table, num);
 	if (!r || sysreg_hidden(vcpu, r))
 		return -ENOENT;
 
···
 
 static bool copy_reg_to_user(const struct sys_reg_desc *reg, u64 __user **uind)
 {
+	u64 idx;
+
 	if (!*uind)
 		return true;
 
-	if (put_user(sys_reg_to_index(reg), *uind))
+	switch (reg_to_encoding(reg)) {
+	case SYS_CNTV_CVAL_EL0:
+		idx = KVM_REG_ARM_TIMER_CVAL;
+		break;
+	case SYS_CNTVCT_EL0:
+		idx = KVM_REG_ARM_TIMER_CNT;
+		break;
+	default:
+		idx = sys_reg_to_index(reg);
+	}
+
+	if (put_user(idx, *uind))
 		return false;
 
 	(*uind)++;

arch/arm64/kvm/sys_regs.h

···
 	(val);								       \
 })
 
+#define TO_ARM64_SYS_REG(r)	ARM64_SYS_REG(sys_reg_Op0(SYS_ ## r),	\
+					      sys_reg_Op1(SYS_ ## r),	\
+					      sys_reg_CRn(SYS_ ## r),	\
+					      sys_reg_CRm(SYS_ ## r),	\
+					      sys_reg_Op2(SYS_ ## r))
+
 #endif /* __ARM64_KVM_SYS_REGS_LOCAL_H__ */