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+