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4b8dcb006e
commit c74cf7a3d59a21b290fe0468f5b470d0b8ee37df upstream.
We currently leak kernel memory to user space, because memory
offlining doesn't do any implicit clearing of memory and we are
missing explicit clearing of memory.
Let's keep it simple and clear pages before removing the linear
mapping.
Reproduced in QEMU/TCG with 10 GiB of main memory:
[root@localhost ~]# dd obs=9G if=/dev/urandom of=/dev/null
[... wait until "free -m" used counter no longer changes and cancel]
19665802+0 records in
1+0 records out
9663676416 bytes (9.7 GB, 9.0 GiB) copied, 135.548 s, 71.3 MB/s
[root@localhost ~]# cat /sys/devices/system/memory/block_size_bytes
40000000
[root@localhost ~]# echo 0x40000000 > /sys/kernel/debug/powerpc/memtrace/enable
[ 402.978663][ T1086] page:000000001bc4bc74 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x24900
[ 402.980063][ T1086] flags: 0x7ffff000001000(reserved)
[ 402.980415][ T1086] raw: 007ffff000001000 c00c000000924008 c00c000000924008 0000000000000000
[ 402.980627][ T1086] raw: 0000000000000000 0000000000000000 00000001ffffffff 0000000000000000
[ 402.980845][ T1086] page dumped because: unmovable page
[ 402.989608][ T1086] Offlined Pages 16384
[ 403.324155][ T1086] memtrace: Allocated trace memory on node 0 at 0x0000000200000000
Before this patch:
[root@localhost ~]# hexdump -C /sys/kernel/debug/powerpc/memtrace/00000000/trace | head
00000000 c8 25 72 51 4d 26 36 c5 5c c2 56 15 d5 1a cd 10 |.%rQM&6.\.V.....|
00000010 19 b9 50 b2 cb e3 60 b8 ec 0a f3 ec 4b 3c 39 f0 |..P...`.....K<9.|$
00000020 4e 5a 4c cf bd 26 19 ff 37 79 13 67 24 b7 b8 57 |NZL..&..7y.g$..W|$
00000030 98 3e f5 be 6f 14 6a bd a4 52 bc 6e e9 e0 c1 5d |.>..o.j..R.n...]|$
00000040 76 b3 ae b5 88 d7 da e3 64 23 85 2c 10 88 07 b6 |v.......d#.,....|$
00000050 9a d8 91 de f7 50 27 69 2e 64 9c 6f d3 19 45 79 |.....P'i.d.o..Ey|$
00000060 6a 6f 8a 61 71 19 1f c7 f1 df 28 26 ca 0f 84 55 |jo.aq.....(&...U|$
00000070 01 3f be e4 e2 e1 da ff 7b 8c 8e 32 37 b4 24 53 |.?......{..27.$S|$
00000080 1b 70 30 45 56 e6 8c c4 0e b5 4c fb 9f dd 88 06 |.p0EV.....L.....|$
00000090 ef c4 18 79 f1 60 b1 5c 79 59 4d f4 36 d7 4a 5c |...y.`.\yYM.6.J\|$
After this patch:
[root@localhost ~]# hexdump -C /sys/kernel/debug/powerpc/memtrace/00000000/trace | head
00000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
40000000
Fixes:
|
||
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.