# git rev-parse -q --verify a58007621be33e9f7c7bed5d5ff8ecb914e1044a^{commit}
a58007621be33e9f7c7bed5d5ff8ecb914e1044a
already have revision, skipping fetch
# git checkout -q -f -B kisskb a58007621be33e9f7c7bed5d5ff8ecb914e1044a
# git clean -qxdf
# < git log -1
# commit a58007621be33e9f7c7bed5d5ff8ecb914e1044a
# 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/gcc-4.6.3-nolibc/powerpc-linux/bin/powerpc-linux-gcc --version
# < /opt/cross/kisskb/gcc-4.6.3-nolibc/powerpc-linux/bin/powerpc-linux-ld --version
# < git log --format=%s --max-count=1 a58007621be33e9f7c7bed5d5ff8ecb914e1044a
# < make -s -j 48 ARCH=powerpc O=/kisskb/build/powerpc-fixes_mpc885_ads_defconfig+HUGETLB_powerpc-gcc4.6 CROSS_COMPILE=/opt/cross/kisskb/gcc-4.6.3-nolibc/powerpc-linux/bin/powerpc-linux-  mpc885_ads_defconfig
# Added to kconfig CONFIG_HUGETLBFS=y
# yes \n | make -s -j 48 ARCH=powerpc O=/kisskb/build/powerpc-fixes_mpc885_ads_defconfig+HUGETLB_powerpc-gcc4.6 CROSS_COMPILE=/opt/cross/kisskb/gcc-4.6.3-nolibc/powerpc-linux/bin/powerpc-linux-  oldconfig
yes: standard output: Broken pipe
# make -s -j 48 ARCH=powerpc O=/kisskb/build/powerpc-fixes_mpc885_ads_defconfig+HUGETLB_powerpc-gcc4.6 CROSS_COMPILE=/opt/cross/kisskb/gcc-4.6.3-nolibc/powerpc-linux/bin/powerpc-linux-  
/kisskb/src/kernel/printk/printk.c: In function 'devkmsg_sysctl_set_loglvl':
/kisskb/src/kernel/printk/printk.c:186:16: warning: 'old' may be used uninitialized in this function [-Wuninitialized]
/kisskb/src/fs/proc/inode.c: In function 'proc_reg_open':
/kisskb/src/include/linux/list.h:65:12: warning: 'pdeo' may be used uninitialized in this function [-Wuninitialized]
/kisskb/src/fs/proc/inode.c:339:21: note: 'pdeo' was declared here
/kisskb/src/mm/hugetlb.c: In function 'alloc_pool_huge_page':
/kisskb/src/mm/hugetlb.c:1434:5: warning: 'page' may be used uninitialized in this function [-Wuninitialized]
Image Name:   Linux-5.0.0-rc1-ga58007621be3
Created:      Sun Feb 17 21:24:17 2019
Image Type:   PowerPC Linux Kernel Image (gzip compressed)
Data Size:    1828957 Bytes = 1786.09 KiB = 1.74 MiB
Load Address: 00400000
Entry Point:  004001dc
Completed OK
# rm -rf /kisskb/build/powerpc-fixes_mpc885_ads_defconfig+HUGETLB_powerpc-gcc4.6
# Build took: 0:00:34.236839