Re: [PATCH] parisc/mm: preallocate fixmap page tables at init

[Helge Deller]

On 8/3/23 08:24, Mike Rapoport wrote:
> From: "Mike Rapoport (IBM)" <rppt@xxxxxxxxxx>
>
> 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
> ...
>      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@xxxxxxxxxx>

Now queued up in parisc for-next tree.

Thanks to Christoph for bisecting and Mike for coming up with this patch!
Helge