KVM: arm64: Do not try to map PUDs when they are folded into PMD

For the obscure cases where PMD and PUD are the same size
(64kB pages with 42bit VA, for example, which results in only
two levels of page tables), we can't map anything as a PUD,
because there is... erm... no PUD to speak of. Everything is
either a PMD or a PTE.

So let's only try and map a PUD when its size is different from
that of a PMD.

Cc: [email protected]
Fixes: b8e0ba7 ("KVM: arm64: Add support for creating PUD hugepages at stage 2")
Reported-by: Gavin Shan <[email protected]>
Reported-by: Eric Auger <[email protected]>
Reviewed-by: Alexandru Elisei <[email protected]>
Reviewed-by: Gavin Shan <[email protected]>
Tested-by: Gavin Shan <[email protected]>
Tested-by: Eric Auger <[email protected]>
Tested-by: Alexandru Elisei <[email protected]>
Signed-off-by: Marc Zyngier <[email protected]>

Author: Marc Zyngier

arch/arm64/kvm/mmu.c

@@ -1964,7 +1964,12 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 		(fault_status == FSC_PERM &&
 		 stage2_is_exec(mmu, fault_ipa, vma_pagesize));
 
-	if (vma_pagesize == PUD_SIZE) {
+	/*
+	 * If PUD_SIZE == PMD_SIZE, there is no real PUD level, and
+	 * all we have is a 2-level page table. Trying to map a PUD in
+	 * this case would be fatally wrong.
+	 */
+	if (PUD_SIZE != PMD_SIZE && vma_pagesize == PUD_SIZE) {
 		pud_t new_pud = kvm_pfn_pud(pfn, mem_type);
 
 		new_pud = kvm_pud_mkhuge(new_pud);