KVM: arm/arm64: Fix idmap size and alignment

Although the idmap section of KVM can only be at most 4kB and
must be aligned on a 4kB boundary, the rest of the code expects
it to be page aligned. Things get messy when tearing down the
HYP page tables when PAGE_SIZE is 64K, and the idmap section isn't
64K aligned.

Let's fix this by computing aligned boundaries that the HYP code
will use.
Acked-by: NCatalin Marinas <catalin.marinas@arm.com>
Reported-by: NJames Morse <james.morse@arm.com>
Reviewed-by: NJames Morse <james.morse@arm.com>
Signed-off-by: NMarc Zyngier <marc.zyngier@arm.com>

virt/kvm/arm/mmu.c

@@ -1815,7 +1815,9 @@ int kvm_mmu_init(void)
 	int err;
 
 	hyp_idmap_start = kvm_virt_to_phys(__hyp_idmap_text_start);
+	hyp_idmap_start = ALIGN_DOWN(hyp_idmap_start, PAGE_SIZE);
 	hyp_idmap_end = kvm_virt_to_phys(__hyp_idmap_text_end);
+	hyp_idmap_end = ALIGN(hyp_idmap_end, PAGE_SIZE);
 	hyp_idmap_vector = kvm_virt_to_phys(__kvm_hyp_init);
 
 	/*