Re: [tip:x86/mm] [x86/mm] 1248fb6a82: Kernel_panic-not_syncing:kasan_populate_pmd:Failed_to_allocate_page

[Yin, Fengwei]

Hi Peter,

On 10/25/2022 6:33 PM, Peter Zijlstra wrote:
> On Tue, Oct 25, 2022 at 12:54:40PM +0800, kernel test robot wrote:
>> Hi Peter,
>>
>> We noticed that below commit changed the value of
>> CPU_ENTRY_AREA_MAP_SIZE. Seems KASAN uses this value to allocate memory,
>> and failed during initialization after this change, so we send this
>> mail and Cc KASAN folks. Please kindly check below report for more
>> details. Thanks.
>>
>>
>> Greeting,
>>
>> FYI, we noticed Kernel_panic-not_syncing:kasan_populate_pmd:Failed_to_allocate_page due to commit (built with gcc-11):
>>
>> commit: 1248fb6a8201ddac1c86a202f05a0a1765efbfce ("x86/mm: Randomize per-cpu entry area")
>> https://git.kernel.org/cgit/linux/kernel/git/tip/tip.git x86/mm
>>
>> in testcase: boot
>>
>> on test machine: qemu-system-x86_64 -enable-kvm -cpu SandyBridge -smp 2 -m 16G
>>
>> caused below changes (please refer to attached dmesg/kmsg for entire log/backtrace):
>>
>>
>> [    7.114808][    T0] Kernel panic - not syncing: kasan_populate_pmd+0x142/0x1d2: Failed to allocate page, nid=0 from=1000000
>> [    7.119742][    T0] CPU: 0 PID: 0 Comm: swapper Not tainted 6.1.0-rc1-00001-g1248fb6a8201 #1
>> [    7.122122][    T0] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.0-debian-1.16.0-4 04/01/2014
>> [    7.124976][    T0] Call Trace:
>> [    7.125849][    T0]  <TASK>
>> [    7.126642][    T0]  ? dump_stack_lvl+0x45/0x5d
>> [    7.127908][    T0]  ? panic+0x21e/0x46a
>> [    7.129009][    T0]  ? panic_print_sys_info+0x77/0x77
>> [    7.130618][    T0]  ? memblock_alloc_try_nid_raw+0x106/0x106
>> [    7.132224][    T0]  ? memblock_alloc_try_nid+0xd9/0x118
>> [    7.133717][    T0]  ? memblock_alloc_try_nid_raw+0x106/0x106
>> [    7.135252][    T0]  ? kasan_populate_pmd+0x142/0x1d2
>> [    7.136655][    T0]  ? early_alloc+0x95/0x9d
>> [    7.137738][    T0]  ? kasan_populate_pmd+0x142/0x1d2
>> [    7.138936][    T0]  ? kasan_populate_pud+0x182/0x19f
>> [    7.140335][    T0]  ? kasan_populate_shadow+0x1e0/0x233
>> [    7.141759][    T0]  ? kasan_init+0x3be/0x57f
>> [    7.142942][    T0]  ? setup_arch+0x101d/0x11f0
>> [    7.144229][    T0]  ? start_kernel+0x6f/0x3d0
>> [    7.145449][    T0]  ? secondary_startup_64_no_verify+0xe0/0xeb
>> [    7.147051][    T0]  </TASK>
>> [    7.147868][    T0] ---[ end Kernel panic - not syncing: kasan_populate_pmd+0x142/0x1d2: Failed to allocate page, nid=0 from=1000000 ]---
> 
> Ufff, no idea about what KASAN wants here; Andrey, you have clue?
> 
> Are you trying to allocate backing space for .5T of vspace and failing
> that because the kvm thing doesn't have enough memory?
Here is what I got when I checked whether this report is valid or not:

KASAN create shadow for cpu entry area:
        shadow_cpu_entry_begin = (void *)CPU_ENTRY_AREA_BASE;
        shadow_cpu_entry_begin = kasan_mem_to_shadow(shadow_cpu_entry_begin);
        shadow_cpu_entry_begin = (void *)round_down(
                        (unsigned long)shadow_cpu_entry_begin, PAGE_SIZE);

        shadow_cpu_entry_end = (void *)(CPU_ENTRY_AREA_BASE +
                                        CPU_ENTRY_AREA_MAP_SIZE);
                                        ^^^^^^^^^^^^^^^^^^^^^^^
        shadow_cpu_entry_end = kasan_mem_to_shadow(shadow_cpu_entry_end);
        shadow_cpu_entry_end = (void *)round_up(
                        (unsigned long)shadow_cpu_entry_end, PAGE_SIZE);

        .....
        kasan_populate_shadow((unsigned long)shadow_cpu_entry_begin,
                              (unsigned long)shadow_cpu_entry_end, 0)

Before the patch, the CPU_ENTRY_AREA_MAP_SIZE is:
  (CPU_ENTRY_AREA_PER_CPU + CPU_ENTRY_AREA_ARRAY_SIZE - CPU_ENTRY_AREA_BASE)

After the patch, it's same for 32bit. But for 64bit, it's: P4D_SIZE.
And trigger kasan_populate_shadow() applied to a very large range.

Hope this info could help somehow. Thanks.

Regards
Yin, Fengwei

>