linux/arch/s390
Gerald Schaefer 723cacbd9d s390/mm: fix asce_bits handling with dynamic pagetable levels
There is a race with multi-threaded applications between context switch and
pagetable upgrade. In switch_mm() a new user_asce is built from mm->pgd and
mm->context.asce_bits, w/o holding any locks. A concurrent mmap with a
pagetable upgrade on another thread in crst_table_upgrade() could already
have set new asce_bits, but not yet the new mm->pgd. This would result in a
corrupt user_asce in switch_mm(), and eventually in a kernel panic from a
translation exception.

Fix this by storing the complete asce instead of just the asce_bits, which
can then be read atomically from switch_mm(), so that it either sees the
old value or the new value, but no mixture. Both cases are OK. Having the
old value would result in a page fault on access to the higher level memory,
but the fault handler would see the new mm->pgd, if it was a valid access
after the mmap on the other thread has completed. So as worst-case scenario
we would have a page fault loop for the racing thread until the next time
slice.

Also remove dead code and simplify the upgrade/downgrade path, there are no
upgrades from 2 levels, and only downgrades from 3 levels for compat tasks.
There are also no concurrent upgrades, because the mmap_sem is held with
down_write() in do_mmap, so the flush and table checks during upgrade can
be removed.

Reported-by: Michael Munday <munday@ca.ibm.com>
Reviewed-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
2016-04-21 09:50:09 +02:00
..
appldata
boot s390/boot/decompression: disable floating point in decompressor 2015-09-29 14:45:10 +02:00
configs s390/configs: update default configurations 2016-01-11 13:01:28 +01:00
crypto Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux 2016-04-01 07:15:54 -05:00
hypfs mm, fs: get rid of PAGE_CACHE_* and page_cache_{get,release} macros 2016-04-04 10:41:08 -07:00
include s390/mm: fix asce_bits handling with dynamic pagetable levels 2016-04-21 09:50:09 +02:00
kernel Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux 2016-04-01 07:15:54 -05:00
kvm Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux 2016-03-16 10:47:45 -07:00
lib s390/spinlock: avoid yield to non existent cpu 2016-04-15 18:01:48 +02:00
mm s390/mm: fix asce_bits handling with dynamic pagetable levels 2016-04-21 09:50:09 +02:00
net bpf: move clearing of A/X into classic to eBPF migration prologue 2015-12-18 16:04:51 -05:00
numa s390/numa: move numa_init_late() from device to arch_initcall 2016-01-26 12:45:24 +01:00
oprofile s390/oprofile: add z13/z13s model numbers 2016-02-24 12:18:10 +01:00
pci s390/pci: fix use after free in dma_init 2016-04-21 09:50:09 +02:00
tools s390/facilities: add helper tool to generate facility lists 2015-12-18 14:59:20 +01:00
defconfig s390/configs: update default configurations 2016-01-11 13:01:28 +01:00
Kbuild s390/numa: add core infrastructure 2015-08-03 18:40:25 +02:00
Kconfig s390: add CPU_BIG_ENDIAN config option 2016-04-15 18:01:52 +02:00
Kconfig.debug arch: consolidate CONFIG_STRICT_DEVM in lib/Kconfig.debug 2016-01-09 06:30:49 -08:00
Makefile s390/facilities: add helper tool to generate facility lists 2015-12-18 14:59:20 +01:00