# git rev-parse -q --verify db2628fc86b6586b3224f91a346d49e8befc5a1f^{commit}
db2628fc86b6586b3224f91a346d49e8befc5a1f
already have revision, skipping fetch
# git checkout -q -f -B kisskb db2628fc86b6586b3224f91a346d49e8befc5a1f
# git clean -qxdf
# < git log -1
# commit db2628fc86b6586b3224f91a346d49e8befc5a1f
# Author: Michael Ellerman <mpe@ellerman.id.au>
# Date:   Thu Feb 14 15:00:36 2019 +1100
# 
#     powerpc/64s: Fix possible corruption on big endian due to pgd/pud_present()
#     
#     In v4.20 we changed our pgd/pud_present() to check for _PAGE_PRESENT
#     rather than just checking that the value is non-zero, e.g.:
#     
#       static inline int pgd_present(pgd_t pgd)
#       {
#      -       return !pgd_none(pgd);
#      +       return (pgd_raw(pgd) & cpu_to_be64(_PAGE_PRESENT));
#       }
#     
#     Unfortunately this is broken on big endian, as the result of the
#     bitwise && is truncated to int, which is always zero because
#     _PAGE_PRESENT is 0x8000000000000000ul. This means pgd_present() and
#     pud_present() are always false at compile time, and the compiler
#     elides the subsequent code.
#     
#     Remarkably with that bug present we are still able to boot and run
#     with few noticeable effects. However under some work loads we are able
#     to trigger a warning in the ext4 code:
#     
#       WARNING: CPU: 11 PID: 29593 at fs/ext4/inode.c:3927 .ext4_set_page_dirty+0x70/0xb0
#       CPU: 11 PID: 29593 Comm: debugedit Not tainted 4.20.0-rc1 #1
#       ...
#       NIP .ext4_set_page_dirty+0x70/0xb0
#       LR  .set_page_dirty+0xa0/0x150
#       Call Trace:
#        .set_page_dirty+0xa0/0x150
#        .unmap_page_range+0xbf0/0xe10
#        .unmap_vmas+0x84/0x130
#        .unmap_region+0xe8/0x190
#        .__do_munmap+0x2f0/0x510
#        .__vm_munmap+0x80/0x110
#        .__se_sys_munmap+0x14/0x30
#        system_call+0x5c/0x70
#     
#     The fix is simple, we need to convert the result of the bitwise && to
#     an int before returning it.
#     
#     Thanks to Erhard, Jan Kara and Aneesh for help with debugging.
#     
#     Fixes: da7ad366b497 ("powerpc/mm/book3s: Update pmd_present to look at _PAGE_PRESENT bit")
#     Cc: stable@vger.kernel.org # v4.20+
#     Reported-by: Erhard F. <erhard_f@mailbox.org>
#     Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.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 db2628fc86b6586b3224f91a346d49e8befc5a1f
# < make -s -j 120 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 120 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-  
Completed OK
# rm -rf /kisskb/build/powerpc-fixes_chrp32_defconfig_powerpc-gcc5
# Build took: 0:00:27.895458