book3s64/hash: Early detect debug_pagealloc size requirement

Add hash_supports_debug_pagealloc() helper to detect whether
debug_pagealloc can be supported on hash or not. This checks for both,
whether debug_pagealloc config is enabled and the linear map should
fit within rma_size/4 region size.

This can then be used early during htab_init_page_sizes() to decide
linear map pagesize if hash supports either debug_pagealloc or
kfence.

Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://patch.msgid.link/c33c6691b2a2cf619cc74ac100118ca4dbf21a48.1729271995.git.ritesh.list@gmail.com

Author: riteshharjani

arch/powerpc/mm/book3s64/hash_utils.c

@@ -329,25 +329,26 @@ static void kernel_unmap_linear_page(unsigned long vaddr, unsigned long idx,
 }
 #endif
 
+static inline bool hash_supports_debug_pagealloc(void)
+{
+	unsigned long max_hash_count = ppc64_rma_size / 4;
+	unsigned long linear_map_count = memblock_end_of_DRAM() >> PAGE_SHIFT;
+
+	if (!debug_pagealloc_enabled() || linear_map_count > max_hash_count)
+		return false;
+	return true;
+}
+
 #ifdef CONFIG_DEBUG_PAGEALLOC
 static u8 *linear_map_hash_slots;
 static unsigned long linear_map_hash_count;
 static DEFINE_RAW_SPINLOCK(linear_map_hash_lock);
 static 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;
+	if (!hash_supports_debug_pagealloc())
 		return;
-	}
 
+	linear_map_hash_count = memblock_end_of_DRAM() >> PAGE_SHIFT;
 	linear_map_hash_slots = memblock_alloc_try_nid(
 			linear_map_hash_count, 1, MEMBLOCK_LOW_LIMIT,
 			ppc64_rma_size,	NUMA_NO_NODE);
@@ -1076,7 +1077,7 @@ static void __init htab_init_page_sizes(void)
 	bool aligned = true;
 	init_hpte_page_sizes();
 
-	if (!debug_pagealloc_enabled() && !kfence_early_init_enabled()) {
+	if (!hash_supports_debug_pagealloc() && !kfence_early_init_enabled()) {
 		/*
 		 * Pick a size for the linear mapping. Currently, we only
 		 * support 16M, 1M and 4K which is the default