book3s64/hash: Remove kfence support temporarily

JIRA: https://issues.redhat.com/browse/RHEL-114396

Conflicts: We found a kernel boot hang on systems using the Hash MMU,
           caused by KFENCE. Instead of backporting the full upstream fix (which involves multiple patches),
           we suggest adding a single patch that disables KFENCE at runtime
           when Hash MMU is enabled. This prevents the boot hang.

           To make the behavior clearer, we added an out-of-tree printk
           so users see an explicit message instead of just kfence_init failed:

           dmesg | grep -Eai "kfence"
           [    0.001193] kfence: not supported with Hash MMU; disabled at runtime.
           [    0.001249] kfence: kfence_init failed

commit 47780e7
Author: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Date:   Fri Oct 18 22:59:43 2024 +0530

    book3s64/hash: Remove kfence support temporarily

    Kfence on book3s Hash on pseries is anyways broken. It fails to boot
    due to RMA size limitation. That is because, kfence with Hash uses
    debug_pagealloc infrastructure. debug_pagealloc allocates linear map
    for entire dram size instead of just kfence relevant objects.
    This means for 16TB of DRAM it will require (16TB >> PAGE_SHIFT)
    which is 256MB which is half of RMA region on P8.
    crash kernel reserves 256MB and we also need 2048 * 16KB * 3 for
    emergency stack and some more for paca allocations.
    That means there is not enough memory for reserving the full linear map
    in the RMA region, if the DRAM size is too big (>=16TB)
    (The issue is seen above 8TB with crash kernel 256 MB reservation).

    Now Kfence does not require linear memory map for entire DRAM.
    It only needs for kfence objects. So this patch temporarily removes the
    kfence functionality since debug_pagealloc code needs some refactoring.
    We will bring in kfence on Hash support in later patches.

    Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
    Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
    Link: https://patch.msgid.link/1761bc39674473c8878dedca15e0d9a0d3a1b528.1729271995.git.ritesh.list@gmail.com

Signed-off-by: Mamatha Inamdar <minamdar@redhat.com>

Author: Mamatha Inamdar

arch/powerpc/include/asm/kfence.h

@@ -10,6 +10,7 @@
 
 #include <linux/mm.h>
 #include <asm/pgtable.h>
+#include <asm/mmu.h>
 
 #ifdef CONFIG_PPC64_ELF_ABI_V1
 #define ARCH_FUNC_PREFIX "."
@@ -25,6 +26,12 @@ static inline void disable_kfence(void)
 
 static inline bool arch_kfence_init_pool(void)
 {
+#ifdef CONFIG_PPC64
+	if (!radix_enabled()) {
+		pr_info("Not supported with Hash MMU; disabled at runtime.\n");
+		return false;
+	}
+#endif
 	return !kfence_disabled;
 }
 #endif

arch/powerpc/mm/book3s64/hash_utils.c

@@ -424,7 +424,7 @@ int htab_bolt_mapping(unsigned long vstart, unsigned long vend,
 			break;
 
 		cond_resched();
-		if (debug_pagealloc_enabled_or_kfence() &&
+		if (debug_pagealloc_enabled() &&
 			(paddr >> PAGE_SHIFT) < linear_map_hash_count)
 			linear_map_hash_slots[paddr >> PAGE_SHIFT] = ret | 0x80;
 	}
@@ -807,7 +807,7 @@ static void __init htab_init_page_sizes(void)
 	bool aligned = true;
 	init_hpte_page_sizes();
 
-	if (!debug_pagealloc_enabled_or_kfence()) {
+	if (!debug_pagealloc_enabled()) {
 		/*
 		 * Pick a size for the linear mapping. Currently, we only
 		 * support 16M, 1M and 4K which is the default
@@ -1127,7 +1127,7 @@ static void __init htab_initialize(void)
 
 	prot = pgprot_val(PAGE_KERNEL);
 
-	if (debug_pagealloc_enabled_or_kfence()) {
+	if (debug_pagealloc_enabled()) {
 		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,
@@ -2110,7 +2110,7 @@ void hpt_do_stress(unsigned long ea, unsigned long hpte_group)
 	}
 }
 
-#if defined(CONFIG_DEBUG_PAGEALLOC) || defined(CONFIG_KFENCE)
+#ifdef CONFIG_DEBUG_PAGEALLOC
 static DEFINE_RAW_SPINLOCK(linear_map_hash_lock);
 
 static void kernel_map_linear_page(unsigned long vaddr, unsigned long lmi)
@@ -2183,7 +2183,13 @@ void hash__kernel_map_pages(struct page *page, int numpages, int enable)
 	}
 	local_irq_restore(flags);
 }
-#endif /* CONFIG_DEBUG_PAGEALLOC || CONFIG_KFENCE */
+#else /* CONFIG_DEBUG_PAGEALLOC */
+void hash__kernel_map_pages(struct page *page, int numpages,
+					 int enable)
+{
+
+}
+#endif /* CONFIG_DEBUG_PAGEALLOC */
 
 void hash__setup_initial_memory_limit(phys_addr_t first_memblock_base,
 				phys_addr_t first_memblock_size)