# git rev-parse -q --verify f41c880e164dc3c9fc3eff6ed27e97583af41986^{commit}
f41c880e164dc3c9fc3eff6ed27e97583af41986
already have revision, skipping fetch
# git checkout -q -f -B kisskb f41c880e164dc3c9fc3eff6ed27e97583af41986
# git clean -qxdf
# < git log -1
# commit f41c880e164dc3c9fc3eff6ed27e97583af41986
# Author: Nicholas Piggin <npiggin@gmail.com>
# Date:   Mon Jun 3 16:05:31 2019 +1000
# 
#     powerpc/64s: Fix THP PMD collapse serialisation
#     
#     Commit 1b2443a547f9 ("powerpc/book3s64: Avoid multiple endian
#     conversion in pte helpers") changed the actual bitwise tests in
#     pte_access_permitted by using pte_write() and pte_present() helpers
#     rather than raw bitwise testing _PAGE_WRITE and _PAGE_PRESENT bits.
#     
#     The pte_present change now returns true for ptes which are
#     !_PAGE_PRESENT and _PAGE_INVALID, which is the combination used by
#     pmdp_invalidate to synchronize access from lock-free lookups.
#     pte_access_permitted is used by pmd_access_permitted, so allowing GUP
#     lock free access to proceed with such PTEs breaks this
#     synchronisation.
#     
#     This bug has been observed on HPT host, with random crashes and
#     corruption in guests, usually together with bad PMD messages in the
#     host.
#     
#     Fix this by adding an explicit check in pmd_access_permitted, and
#     documenting the condition explicitly.
#     
#     The pte_write() change should be okay, and would prevent GUP from
#     falling back to the slow path when encountering savedwrite ptes, which
#     matches what x86 (that does not implement savedwrite) does.
#     
#     Fixes: 1b2443a547f9 ("powerpc/book3s64: Avoid multiple endian conversion in pte helpers")
#     Cc: stable@vger.kernel.org # v4.20+
#     Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
#     Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
# < /opt/cross/kisskb/korg/gcc-5.5.0-nolibc/powerpc64-linux/bin/powerpc64-linux-gcc --version
# < /opt/cross/kisskb/korg/gcc-5.5.0-nolibc/powerpc64-linux/bin/powerpc64-linux-ld --version
# < git log --format=%s --max-count=1 f41c880e164dc3c9fc3eff6ed27e97583af41986
# < make -s -j 48 ARCH=powerpc O=/kisskb/build/powerpc-fixes_chrp32_defconfig_powerpc-gcc5 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-5.5.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  chrp32_defconfig
# make -s -j 48 ARCH=powerpc O=/kisskb/build/powerpc-fixes_chrp32_defconfig_powerpc-gcc5 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-5.5.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  
/kisskb/src/kernel/futex.c: In function 'do_futex':
/kisskb/src/kernel/futex.c:1658:17: warning: 'oldval' may be used uninitialized in this function [-Wmaybe-uninitialized]
   return oldval == cmparg;
                 ^
/kisskb/src/kernel/futex.c:1633:6: note: 'oldval' was declared here
  int oldval, ret;
      ^
warning: same basename if the following are built as modules:
  arch/powerpc/platforms/chrp/nvram.ko
  drivers/char/nvram.ko
Completed OK
# rm -rf /kisskb/build/powerpc-fixes_chrp32_defconfig_powerpc-gcc5
# Build took: 0:00:44.221773