linux_dsm_epyc7002/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
configs
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
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
numa
oprofile
pci s390/pci: fix use after free in dma_init 2016-04-21 09:50:09 +02:00
tools
defconfig
Kbuild
Kconfig s390: add CPU_BIG_ENDIAN config option 2016-04-15 18:01:52 +02:00
Kconfig.debug
Makefile