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Gerald Schaefer 5f490a520b s390/mm: fix dynamic pagetable upgrade for hugetlbfs 
Commit ee71d16d22 ("s390/mm: make TASK_SIZE independent from the number
of page table levels") changed the logic of TASK_SIZE and also removed the
arch_mmap_check() implementation for s390. This combination has a subtle
effect on how get_unmapped_area() for hugetlbfs pages works. It is now
possible that a user process establishes a hugetlbfs mapping at an address
above 4 TB, without triggering a dynamic pagetable upgrade from 3 to 4
levels.

This is because hugetlbfs mappings will not use mm->get_unmapped_area, but
rather file->f_op->get_unmapped_area, which currently is the generic
implementation of hugetlb_get_unmapped_area() that does not know about s390
dynamic pagetable upgrades, but with the new definition of TASK_SIZE, it
will now allow mappings above 4 TB.

Subsequent access to such a mapped address above 4 TB will result in a page
fault loop, because the CPU cannot translate such a large address with 3
pagetable levels. The fault handler will try to map in a hugepage at the
address, but due to the folded pagetable logic it will end up with creating
entries in the 3 level pagetable, possibly overwriting existing mappings,
and then it all repeats when the access is retried.

Apart from the page fault loop, this can have various nasty effects, e.g.
kernel panic from one of the BUG_ON() checks in memory management code,
or even data loss if an existing mapping gets overwritten.

Fix this by implementing HAVE_ARCH_HUGETLB_UNMAPPED_AREA support for s390,
providing an s390 version for hugetlb_get_unmapped_area() with pagetable
upgrade support similar to arch_get_unmapped_area(), which will then be
used instead of the generic version.

Fixes: ee71d16d22 ("s390/mm: make TASK_SIZE independent from the number of page table levels")
Cc: <stable@vger.kernel.org> # 4.12+
Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
2020-01-30 13:07:54 +01:00
arch s390/mm: fix dynamic pagetable upgrade for hugetlbfs 2020-01-30 13:07:54 +01:00
block for-5.6/block-2020-01-27 2020-01-27 12:38:25 -08:00
certs certs: Add wrapper function to check blacklisted binary hash 2019-11-12 12:25:50 +11:00
crypto Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2020-01-28 15:38:56 -08:00
Documentation - Depromote debug print on the db8500 platform (Linus Walleij) 2020-01-28 16:31:08 -08:00
drivers - Depromote debug print on the db8500 platform (Linus Walleij) 2020-01-28 16:31:08 -08:00
fs Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2020-01-28 15:38:56 -08:00
include - Depromote debug print on the db8500 platform (Linus Walleij) 2020-01-28 16:31:08 -08:00
init This pull request contains the following changes for UML: 2020-01-28 18:29:25 -08:00
ipc treewide: Use sizeof_field() macro 2019-12-09 10:36:44 -08:00
kernel This pull request contains the following changes for UML: 2020-01-28 18:29:25 -08:00
lib Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next 2020-01-28 16:02:33 -08:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
mm for-5.6-tag 2020-01-28 14:53:31 -08:00
net Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next 2020-01-28 16:02:33 -08:00
samples Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next 2020-01-28 16:02:33 -08:00
scripts Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next 2020-01-28 16:02:33 -08:00
security Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next 2020-01-28 16:02:33 -08:00
sound sound updates for 5.6-rc1 2020-01-28 16:26:57 -08:00
tools Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next 2020-01-28 16:02:33 -08:00
usr gen_initramfs_list.sh: fix 'bad variable name' error 2020-01-04 00:00:48 +09:00
virt PPC KVM fix for 5.5 2019-12-22 13:18:15 +01:00
.clang-format clang-format: Update with the latest for_each macro list 2019-08-31 10:00:51 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore modpost: dump missing namespaces into a single modules.nsdeps file 2019-11-11 20:10:01 +09:00
.mailmap Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2020-01-28 15:38:56 -08:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS Linux 5.4-rc4 2019-10-29 04:43:29 -06:00
Kbuild kbuild: do not descend to ./Kbuild when cleaning 2019-08-21 21:03:58 +09:00
Kconfig docs: kbuild: convert docs to ReST and rename to *.rst 2019-06-14 14:21:21 -06:00
MAINTAINERS - Depromote debug print on the db8500 platform (Linus Walleij) 2020-01-28 16:31:08 -08:00
Makefile Linux 5.5 2020-01-26 16:23:03 -08:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

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.