KVM: arm64: Access CNTHCTL_EL2 bit fields correctly on VHE systems

Current KVM world switch code is unintentionally setting wrong bits to
CNTHCTL_EL2 when E2H == 1, which may allow guest OS to access physical
timer.  Bit positions of CNTHCTL_EL2 are changing depending on
HCR_EL2.E2H bit.  EL1PCEN and EL1PCTEN are 1st and 0th bits when E2H is
not set, but they are 11th and 10th bits respectively when E2H is set.

In fact, on VHE we only need to set those bits once, not for every world
switch. This is because the host kernel runs in EL2 with HCR_EL2.TGE ==
1, which makes those bits have no effect for the host kernel execution.
So we just set those bits once for guests, and that's it.

Signed-off-by: Jintack Lim <jintack@cs.columbia.edu>
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

arch/arm/include/asm/virt.h

@@ -80,6 +80,11 @@ static inline bool is_kernel_in_hyp_mode(void)
 	return false;
 }
 
+static inline bool has_vhe(void)
+{
+	return false;
+}
+
 /* The section containing the hypervisor idmap text */
 extern char __hyp_idmap_text_start[];
 extern char __hyp_idmap_text_end[];