book3s64/hash: Disable debug_pagealloc if it requires more memory

Make size of the linear map to be allocated in RMA region to be of
ppc64_rma_size / 4. If debug_pagealloc requires more memory than that
then do not allocate any memory and disable debug_pagealloc.

Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://patch.msgid.link/e1ef66f32a1fe63bcbb89d5c11d86c65beef5ded.1729271995.git.ritesh.list@gmail.com

arch/powerpc/mm/book3s64/hash_utils.c

@@ -331,9 +331,19 @@ static unsigned long linear_map_hash_count;
 static DEFINE_RAW_SPINLOCK(linear_map_hash_lock);
 static inline void hash_debug_pagealloc_alloc_slots(void)
 {
+	unsigned long max_hash_count = ppc64_rma_size / 4;
+
 	if (!debug_pagealloc_enabled())
 		return;
 	linear_map_hash_count = memblock_end_of_DRAM() >> PAGE_SHIFT;
+	if (unlikely(linear_map_hash_count > max_hash_count)) {
+		pr_info("linear map size (%llu) greater than 4 times RMA region (%llu). Disabling debug_pagealloc\n",
+			((u64)linear_map_hash_count << PAGE_SHIFT),
+			ppc64_rma_size);
+		linear_map_hash_count = 0;
+		return;
+	}
+
 	linear_map_hash_slots = memblock_alloc_try_nid(
 			linear_map_hash_count, 1, MEMBLOCK_LOW_LIMIT,
 			ppc64_rma_size,	NUMA_NO_NODE);
@@ -344,7 +354,7 @@ static inline void hash_debug_pagealloc_alloc_slots(void)
 
 static inline void hash_debug_pagealloc_add_slot(phys_addr_t paddr, int slot)
 {
-	if (!debug_pagealloc_enabled())
+	if (!debug_pagealloc_enabled() || !linear_map_hash_count)
 		return;
 	if ((paddr >> PAGE_SHIFT) < linear_map_hash_count)
 		linear_map_hash_slots[paddr >> PAGE_SHIFT] = slot | 0x80;
@@ -356,6 +366,9 @@ static int hash_debug_pagealloc_map_pages(struct page *page, int numpages,
 	unsigned long flags, vaddr, lmi;
 	int i;
 
+	if (!debug_pagealloc_enabled() || !linear_map_hash_count)
+		return 0;
+
 	local_irq_save(flags);
 	for (i = 0; i < numpages; i++, page++) {
 		vaddr = (unsigned long)page_address(page);