ARM: KVM: add missing dsb before invalidating Stage-2 TLBs

When performing a Stage-2 TLB invalidation, it is necessary to
make sure the write to the page tables is observable by all CPUs.

For this purpose, add a dsb instruction to __kvm_tlb_flush_vmid_ipa
before doing the TLB invalidation itself.
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>

arch/arm/kvm/interrupts.S

@@ -49,6 +49,7 @@ __kvm_hyp_code_start:
 ENTRY(__kvm_tlb_flush_vmid_ipa)
 	push	{r2, r3}
 
+	dsb	ishst
 	add	r0, r0, #KVM_VTTBR
 	ldrd	r2, r3, [r0]
 	mcrr	p15, 6, r2, r3, c2	@ Write VTTBR