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Date:   Tue, 13 Mar 2018 23:43:35 +0000
From:   Sasha Levin <Alexander.Levin@...rosoft.com>
To:     Pavel Tatashin <pasha.tatashin@...cle.com>
CC:     "steven.sistare@...cle.com" <steven.sistare@...cle.com>,
        "daniel.m.jordan@...cle.com" <daniel.m.jordan@...cle.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "mgorman@...hsingularity.net" <mgorman@...hsingularity.net>,
        "mhocko@...e.com" <mhocko@...e.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "vbabka@...e.cz" <vbabka@...e.cz>,
        "bharata@...ux.vnet.ibm.com" <bharata@...ux.vnet.ibm.com>
Subject: Re: [PATCH v2 1/2] mm: uninitialized struct page poisoning sanity
 checking

On Wed, Jan 31, 2018 at 04:02:59PM -0500, Pavel Tatashin wrote:
>During boot we poison struct page memory in order to ensure that no one is
>accessing this memory until the struct pages are initialized in
>__init_single_page().
>
>This patch adds more scrutiny to this checking, by making sure that flags
>do not equal to poison pattern when the are accessed. The pattern is all
>ones.
>
>Since, node id is also stored in struct page, and may be accessed quiet
>early we add the enforcement into page_to_nid() function as well.
>
>Signed-off-by: Pavel Tatashin <pasha.tatashin@...cle.com>
>---

Hey Pasha,

This patch is causing the following on boot:

[    1.253732] BUG: unable to handle kernel paging request at fffffffffffffffe
[    1.254000] PGD 2284e19067 P4D 2284e19067 PUD 2284e1b067 PMD 0
[    1.254000] Oops: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN PTI
[    1.254000] Modules linked in:
[    1.254000] CPU: 1 PID: 1 Comm: swapper/0 Not tainted 4.16.0-rc5-next-20180313 #10
[    1.254000] Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine, BIOS 090007  06/02/2017
[    1.254000] RIP: 0010:__dump_page (??:?)
[    1.254000] RSP: 0000:ffff881c63c17810 EFLAGS: 00010246
[    1.254000] RAX: dffffc0000000000 RBX: ffffea0084000000 RCX: 1ffff1038c782f2b
[    1.254000] RDX: 1fffffffffffffff RSI: ffffffff9e160640 RDI: ffffea0084000000
[    1.254000] RBP: ffff881c63c17c00 R08: ffff8840107e8880 R09: ffffed0802167a4d
[    1.254000] R10: 0000000000000001 R11: ffffed0802167a4c R12: 1ffff1038c782f07
[    1.254000] R13: ffffea0084000020 R14: fffffffffffffffe R15: ffff881c63c17bd8
[    1.254000] FS:  0000000000000000(0000) GS:ffff881c6ac00000(0000) knlGS:0000000000000000
[    1.254000] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    1.254000] CR2: fffffffffffffffe CR3: 0000002284e16000 CR4: 00000000003406e0
[    1.254000] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[    1.254000] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[    1.254000] Call Trace:
[    1.254000] dump_page (/mm/debug.c:80)
[    1.254000] get_nid_for_pfn (/./include/linux/mm.h:900 /drivers/base/node.c:396)
[    1.254000] register_mem_sect_under_node (/drivers/base/node.c:438)
[    1.254000] link_mem_sections (/drivers/base/node.c:517)
[    1.254000] topology_init (/./include/linux/nodemask.h:271 /arch/x86/kernel/topology.c:164)
[    1.254000] do_one_initcall (/init/main.c:835)
[    1.254000] kernel_init_freeable (/init/main.c:901 /init/main.c:909 /init/main.c:927 /init/main.c:1076)
[    1.254000] kernel_init (/init/main.c:1004)
[    1.254000] ret_from_fork (/arch/x86/entry/entry_64.S:417)
[ 1.254000] Code: ff a8 01 4c 0f 44 f3 4d 85 f6 0f 84 31 0e 00 00 4c 89 f2 48 b8 00 00 00 00 00 fc ff df 48 c1 ea 03 80 3c 02 00 0f 85 2d 11 00 00 <49> 83 3e ff 0f 84 a9 06 00 00 4d 8d b7 c0 fd ff ff 48 b8 00 00
All code
========
   0:   ff a8 01 4c 0f 44       ljmp   *0x440f4c01(%rax)
   6:   f3 4d 85 f6             repz test %r14,%r14
   a:   0f 84 31 0e 00 00       je     0xe41
  10:   4c 89 f2                mov    %r14,%rdx
  13:   48 b8 00 00 00 00 00    movabs $0xdffffc0000000000,%rax
  1a:   fc ff df
  1d:   48 c1 ea 03             shr    $0x3,%rdx
  21:   80 3c 02 00             cmpb   $0x0,(%rdx,%rax,1)
  25:   0f 85 2d 11 00 00       jne    0x1158
  2b:*  49 83 3e ff             cmpq   $0xffffffffffffffff,(%r14)               <-- trapping instruction
  2f:   0f 84 a9 06 00 00       je     0x6de
  35:   4d 8d b7 c0 fd ff ff    lea    -0x240(%r15),%r14
  3c:   48                      rex.W
  3d:   b8                      .byte 0xb8
        ...

Code starting with the faulting instruction
===========================================
   0:   49 83 3e ff             cmpq   $0xffffffffffffffff,(%r14)
   4:   0f 84 a9 06 00 00       je     0x6b3
   a:   4d 8d b7 c0 fd ff ff    lea    -0x240(%r15),%r14
  11:   48                      rex.W
  12:   b8                      .byte 0xb8
        ...
[    1.254000] RIP: __dump_page+0x1c8/0x13c0 RSP: ffff881c63c17810 (/./include/asm-generic/sections.h:42)
[    1.254000] CR2: fffffffffffffffe
[    1.254000] ---[ end trace e643dfbc44b562ca ]---

-- 

Thanks,
Sasha

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