# git rev-parse -q --verify 81b654c273914704a4bdf580f28d67aaba1094e4^{commit}
81b654c273914704a4bdf580f28d67aaba1094e4
already have revision, skipping fetch
# git checkout -q -f -B kisskb 81b654c273914704a4bdf580f28d67aaba1094e4
# git clean -qxdf
# < git log -1
# commit 81b654c273914704a4bdf580f28d67aaba1094e4
# Author: Michael Ellerman <mpe@ellerman.id.au>
# Date:   Thu Apr 12 22:24:45 2018 +1000
# 
#     powerpc/64s: Fix CPU_FTRS_ALWAYS vs DT CPU features
#     
#     The cpu_has_feature() mechanism has an optimisation where at build
#     time we construct a mask of the CPU feature bits that will always be
#     true for the given .config, based on the platform/bitness/etc. that we
#     are building for.
#     
#     That is incompatible with DT CPU features, where the set of CPU
#     features is dependent on feature flags that are given to us by
#     firmware.
#     
#     The result is that some feature bits can not be *disabled* by DT CPU
#     features. Or more accurately, they can be disabled but they will still
#     appear in the ALWAYS mask, meaning cpu_has_feature() will always
#     return true for them.
#     
#     In the past this hasn't really been a problem because on Book3S
#     64 (where we support DT CPU features), the set of ALWAYS bits has been
#     very small. That was because we always built for POWER4 and later,
#     meaning the set of common bits was small.
#     
#     The only bit that could be cleared by DT CPU features that was also in
#     the ALWAYS mask was CPU_FTR_NODSISRALIGN, and that was only used in
#     the alignment handler to create a fake DSISR. That code was itself
#     deleted in 31bfdb036f12 ("powerpc: Use instruction emulation
#     infrastructure to handle alignment faults") (Sep 2017).
#     
#     However the set of ALWAYS features changed with the recent commit
#     db5ae1c155af ("powerpc/64s: Refine feature sets for little endian
#     builds") which restricted the set of feature flags when building
#     little endian to Power7 or later. That caused the ALWAYS mask to
#     become much larger for little endian builds.
#     
#     The result is that the following feature bits can currently not
#     be *disabled* by DT CPU features:
#     
#       CPU_FTR_REAL_LE, CPU_FTR_MMCRA, CPU_FTR_CTRL, CPU_FTR_SMT,
#       CPU_FTR_PURR, CPU_FTR_SPURR, CPU_FTR_DSCR, CPU_FTR_PKEY,
#       CPU_FTR_VMX_COPY, CPU_FTR_CFAR, CPU_FTR_HAS_PPR.
#     
#     To fix it we need to mask the set of ALWAYS features with the base set
#     of DT CPU features, ie. the features that are always enabled by DT CPU
#     features. That way there are no bits in the ALWAYS mask that are not
#     also always set by DT CPU features.
#     
#     Fixes: db5ae1c155af ("powerpc/64s: Refine feature sets for little endian builds")
#     Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
#     Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
# < /opt/cross/kisskb/gcc-5.3.0-nolibc/powerpc64-linux/bin/powerpc64-linux-gcc --version
# < git log --format=%s --max-count=1 81b654c273914704a4bdf580f28d67aaba1094e4
# < make -s -j 80 ARCH=powerpc O=/kisskb/build/powerpc-fixes_83xx_mpc8315_rdb_defconfig_powerpc-5.3 CROSS_COMPILE=/opt/cross/kisskb/gcc-5.3.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  83xx/mpc8315_rdb_defconfig
# make -s -j 80 ARCH=powerpc O=/kisskb/build/powerpc-fixes_83xx_mpc8315_rdb_defconfig_powerpc-5.3 CROSS_COMPILE=/opt/cross/kisskb/gcc-5.3.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  
INFO: Uncompressed kernel (size 0x5aa208) overlaps the address of the wrapper(0x400000)
INFO: Fixing the link_address of wrapper to (0x600000)
Image Name:   Linux-4.16.0-g81b654c
Created:      Sat Apr 14 01:36:56 2018
Image Type:   PowerPC Linux Kernel Image (gzip compressed)
Data Size:    2891061 Bytes = 2823.30 kB = 2.76 MB
Load Address: 00000000
Entry Point:  00000000
Completed OK
# rm -rf /kisskb/build/powerpc-fixes_83xx_mpc8315_rdb_defconfig_powerpc-5.3
# Build took: 0:00:43.100935