powerpc/64s: Allow double call of kernel_[un]map_linear_page()

If the page is already mapped resp. already unmapped, bail out.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Nicholas Miehlbradt <nicholas@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220926075726.2846-3-nicholas@linux.ibm.com

arch/powerpc/mm/book3s64/hash_utils.c

@@ -1997,6 +1997,9 @@ static void kernel_map_linear_page(unsigned long vaddr, unsigned long lmi)
 	if (!vsid)
 		return;
 
+	if (linear_map_hash_slots[lmi] & 0x80)
+		return;
+
 	ret = hpte_insert_repeating(hash, vpn, __pa(vaddr), mode,
 				    HPTE_V_BOLTED,
 				    mmu_linear_psize, mmu_kernel_ssize);
@@ -2016,7 +2019,10 @@ static void kernel_unmap_linear_page(unsigned long vaddr, unsigned long lmi)
 
 	hash = hpt_hash(vpn, PAGE_SHIFT, mmu_kernel_ssize);
 	spin_lock(&linear_map_hash_lock);
-	BUG_ON(!(linear_map_hash_slots[lmi] & 0x80));
+	if (!(linear_map_hash_slots[lmi] & 0x80)) {
+		spin_unlock(&linear_map_hash_lock);
+		return;
+	}
 	hidx = linear_map_hash_slots[lmi] & 0x7f;
 	linear_map_hash_slots[lmi] = 0;
 	spin_unlock(&linear_map_hash_lock);