parisc/mm: preallocate fixmap page tables at init

Christoph Biedl reported early OOM on recent kernels:

    swapper: page allocation failure: order:0, mode:0x100(__GFP_ZERO),
nodemask=(null)
    CPU: 0 PID: 0 Comm: swapper Not tainted 6.3.0-rc4+ #16
    Hardware name: 9000/785/C3600
    Backtrace:
     [<10408594>] show_stack+0x48/0x5c
     [<10e152d8>] dump_stack_lvl+0x48/0x64
     [<10e15318>] dump_stack+0x24/0x34
     [<105cf7f8>] warn_alloc+0x10c/0x1c8
     [<105d068c>] __alloc_pages+0xbbc/0xcf8
     [<105d0e4c>] __get_free_pages+0x28/0x78
     [<105ad10c>] __pte_alloc_kernel+0x30/0x98
     [<10406934>] set_fixmap+0xec/0xf4
     [<10411ad4>] patch_map.constprop.0+0xa8/0xdc
     [<10411bb0>] __patch_text_multiple+0xa8/0x208
     [<10411d78>] patch_text+0x30/0x48
     [<1041246c>] arch_jump_label_transform+0x90/0xcc
     [<1056f734>] jump_label_update+0xd4/0x184
     [<1056fc9c>] static_key_enable_cpuslocked+0xc0/0x110
     [<1056fd08>] static_key_enable+0x1c/0x2c
     [<1011362c>] init_mem_debugging_and_hardening+0xdc/0xf8
     [<1010141c>] start_kernel+0x5f0/0xa98
     [<10105da8>] start_parisc+0xb8/0xe4

    Mem-Info:
    active_anon:0 inactive_anon:0 isolated_anon:0
     active_file:0 inactive_file:0 isolated_file:0
     unevictable:0 dirty:0 writeback:0
     slab_reclaimable:0 slab_unreclaimable:0
     mapped:0 shmem:0 pagetables:0
     sec_pagetables:0 bounce:0
     kernel_misc_reclaimable:0
     free:0 free_pcp:0 free_cma:0
    Node 0 active_anon:0kB inactive_anon:0kB active_file:0kB
inactive_file:0kB unevictable:0kB isolated(anon):0kB isolated(file):0kB
mapped:0kB dirty:0kB writeback:0kB shmem:0kB
+writeback_tmp:0kB kernel_stack:0kB pagetables:0kB sec_pagetables:0kB
all_unreclaimable? no
    Normal free:0kB boost:0kB min:0kB low:0kB high:0kB
reserved_highatomic:0KB active_anon:0kB inactive_anon:0kB active_file:0kB
inactive_file:0kB unevictable:0kB writepending:0kB
+present:1048576kB managed:1039360kB mlocked:0kB bounce:0kB free_pcp:0kB
local_pcp:0kB free_cma:0kB
    lowmem_reserve[]: 0 0
    Normal: 0*4kB 0*8kB 0*16kB 0*32kB 0*64kB 0*128kB 0*256kB 0*512kB
0*1024kB 0*2048kB 0*4096kB = 0kB
    0 total pagecache pages
    0 pages in swap cache
    Free swap  = 0kB
    Total swap = 0kB
    262144 pages RAM
    0 pages HighMem/MovableOnly
    2304 pages reserved
    Backtrace:
     [<10411d78>] patch_text+0x30/0x48
     [<1041246c>] arch_jump_label_transform+0x90/0xcc
     [<1056f734>] jump_label_update+0xd4/0x184
     [<1056fc9c>] static_key_enable_cpuslocked+0xc0/0x110
     [<1056fd08>] static_key_enable+0x1c/0x2c
     [<1011362c>] init_mem_debugging_and_hardening+0xdc/0xf8
     [<1010141c>] start_kernel+0x5f0/0xa98
     [<10105da8>] start_parisc+0xb8/0xe4

    Kernel Fault: Code=15 (Data TLB miss fault) at addr 0f7fe3c0
    CPU: 0 PID: 0 Comm: swapper Not tainted 6.3.0-rc4+ #16
    Hardware name: 9000/785/C3600

This happens because patching static key code temporarily maps it via
fixmap and if it happens before page allocator is initialized set_fixmap()
cannot allocate memory using pte_alloc_kernel().

Make sure that fixmap page tables are preallocated early so that
pte_offset_kernel() in set_fixmap() never resorts to pte allocation.
Signed-off-by: Mike Rapoport (IBM) <rppt@kernel.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Helge Deller <deller@gmx.de>
Tested-by: Christoph Biedl <linux-kernel.bfrz@manchmal.in-ulm.de>
Tested-by: John David Anglin <dave.anglin@bell.net>
Cc: <stable@vger.kernel.org> # v6.4+

arch/parisc/mm/fixmap.c

@@ -19,9 +19,6 @@ void notrace set_fixmap(enum fixed_addresses idx, phys_addr_t phys)
 	pmd_t *pmd = pmd_offset(pud, vaddr);
 	pte_t *pte;
 
-	if (pmd_none(*pmd))
-		pte = pte_alloc_kernel(pmd, vaddr);
-
 	pte = pte_offset_kernel(pmd, vaddr);
 	set_pte_at(&init_mm, vaddr, pte, __mk_pte(phys, PAGE_KERNEL_RWX));
 	flush_tlb_kernel_range(vaddr, vaddr + PAGE_SIZE);

arch/parisc/mm/init.c

@@ -669,6 +669,39 @@ static void __init gateway_init(void)
 		  PAGE_SIZE, PAGE_GATEWAY, 1);
 }
 
+static void __init fixmap_init(void)
+{
+	unsigned long addr = FIXMAP_START;
+	unsigned long end = FIXMAP_START + FIXMAP_SIZE;
+	pgd_t *pgd = pgd_offset_k(addr);
+	p4d_t *p4d = p4d_offset(pgd, addr);
+	pud_t *pud = pud_offset(p4d, addr);
+	pmd_t *pmd;
+
+	BUILD_BUG_ON(FIXMAP_SIZE > PMD_SIZE);
+
+#if CONFIG_PGTABLE_LEVELS == 3
+	if (pud_none(*pud)) {
+		pmd = memblock_alloc(PAGE_SIZE << PMD_TABLE_ORDER,
+				     PAGE_SIZE << PMD_TABLE_ORDER);
+		if (!pmd)
+			panic("fixmap: pmd allocation failed.\n");
+		pud_populate(NULL, pud, pmd);
+	}
+#endif
+
+	pmd = pmd_offset(pud, addr);
+	do {
+		pte_t *pte = memblock_alloc(PAGE_SIZE, PAGE_SIZE);
+		if (!pte)
+			panic("fixmap: pte allocation failed.\n");
+
+		pmd_populate_kernel(&init_mm, pmd, pte);
+
+		addr += PAGE_SIZE;
+	} while (addr < end);
+}
+
 static void __init parisc_bootmem_free(void)
 {
 	unsigned long max_zone_pfn[MAX_NR_ZONES] = { 0, };
@@ -683,6 +716,7 @@ void __init paging_init(void)
 	setup_bootmem();
 	pagetable_init();
 	gateway_init();
+	fixmap_init();
 	flush_cache_all_local(); /* start with known state */
 	flush_tlb_all_local(NULL);