Re: [PATCH] x86: mm: Check if PUD is large when validating a kernel address v2

[Simon Jeons <simon.jeons@gmail.com>]

On 03/01/2013 05:15 PM, Chen Gong wrote:
> On Fri, Mar 01, 2013 at 02:43:53PM +0800, Simon Jeons wrote:
>> Date: Fri, 01 Mar 2013 14:43:53 +0800
>> From: Simon Jeons <simon.jeons@gmail.com>
>> To: Mel Gorman <mgorman@suse.de>
>> CC: Ingo Molnar <mingo@kernel.org>, Andrew Morton
>>   <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org,
>>   linux-mm@kvack.org, riel@redhat.com, mhocko@suse.cz, hannes@cmpxchg.org
>> Subject: Re: [PATCH] x86: mm: Check if PUD is large when validating a
>>   kernel address v2
>> User-Agent: Mozilla/5.0 (X11; Linux i686; rv:17.0) Gecko/20130221
>>   Thunderbird/17.0.3
>>
>> On 02/13/2013 07:02 PM, Mel Gorman wrote:
>>> Andrew or Ingo, please pick up.
>>>
>>> Changelog since v1
>>>    o Add reviewed-bys and acked-bys
>>>
>>> A user reported a bug whereby a backup process accessing /proc/kcore
>>> caused an oops.
>>>
>>>   BUG: unable to handle kernel paging request at ffffbb00ff33b000
>>>   IP: [<ffffffff8103157e>] kern_addr_valid+0xbe/0x110
>>>   PGD 0
>>>   Oops: 0000 [#1] SMP
>>>   CPU 6
>>>   Modules linked in: af_packet nfs lockd fscache auth_rpcgss nfs_acl sunrpc 8021q garp stp llc cpufreq_conservative cpufreq_userspace cpufreq_powersave acpi_cpufreq mperf microcode fuse nls_iso8859_1 nls_cp437 vfat fat loop dm_mod ioatdma ipv6 ipv6_lib igb dca i7core_edac edac_core i2c_i801 i2c_core cdc_ether usbnet bnx2 mii iTCO_wdt iTCO_vendor_support shpchp rtc_cmos pci_hotplug tpm_tis sg tpm pcspkr tpm_bios serio_raw button ext3 jbd mbcache uhci_hcd ehci_hcd usbcore sd_mod crc_t10dif usb_common processor thermal_sys hwmon scsi_dh_emc scsi_dh_rdac scsi_dh_alua scsi_dh_hp_sw scsi_dh ata_generic ata_piix libata megaraid_sas scsi_mod
>>>
>>>   Pid: 16196, comm: Hibackp Not tainted 3.0.13-0.27-default #1 IBM System x3550 M3 -[7944 K3G]-/94Y7614
>>>   RIP: 0010:[<ffffffff8103157e>]  [<ffffffff8103157e>] kern_addr_valid+0xbe/0x110
>>>   RSP: 0018:ffff88094165fe80  EFLAGS: 00010246
>>>   RAX: 00003300ff33b000 RBX: ffff880100000000 RCX: 0000000000000000
>>>   RDX: 0000000100000000 RSI: ffff880000000000 RDI: ff32b300ff33b400
>>>   RBP: 0000000000001000 R08: 00003ffffffff000 R09: 0000000000000000
>>>   R10: 22302e31223d6e6f R11: 0000000000000246 R12: 0000000000001000
>>>   R13: 0000000000003000 R14: 0000000000571be0 R15: ffff88094165ff50
>>>   FS:  00007ff152d33700(0000) GS:ffff88097f2c0000(0000) knlGS:0000000000000000
>>>   CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
>>>   CR2: ffffbb00ff33b000 CR3: 00000009405a3000 CR4: 00000000000006e0
>>>   DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>>>   DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
>>>   Process Hibackp (pid: 16196, threadinfo ffff88094165e000, task ffff8808eb9ba600)
>>>   Stack:
>>>    ffffffff811b8aaa 0000000000004000 ffff880943fea480 ffff8808ef2bae50
>>>    ffff880943d32980 fffffffffffffffb ffff8808ef2bae40 ffff88094165ff50
>>>    0000000000004000 000000000056ebe0 ffffffff811ad847 000000000056ebe0
>>>   Call Trace:
>>>    [<ffffffff811b8aaa>] read_kcore+0x17a/0x370
>>>    [<ffffffff811ad847>] proc_reg_read+0x77/0xc0
>>>    [<ffffffff81151687>] vfs_read+0xc7/0x130
>>>    [<ffffffff811517f3>] sys_read+0x53/0xa0
>>>    [<ffffffff81449692>] system_call_fastpath+0x16/0x1b
>>>
>>> Investigation determined that the bug triggered when reading system RAM
>>> at the 4G mark. On this system, that was the first address using 1G pages
>> Do you mean there is one page which is 1G?
>>
> 1GB support in native kernel is started from 2.6.27 with these 2 commits:

Why call kernel native? Which kend of kernel is not native?

> 39c11e6 and b4718e6. For Intel CPU, from Westmere it supports 1GB page.
> BTW, IBM System x3550 M3 is a Westmere based system.
Is it only used in hugetlbfs page?