# git rev-parse -q --verify e620d45065c7b5b8d6ae11217c09c09380103b83^{commit}
e620d45065c7b5b8d6ae11217c09c09380103b83
already have revision, skipping fetch
# git checkout -q -f -B kisskb e620d45065c7b5b8d6ae11217c09c09380103b83
# git clean -qxdf
# < git log -1
# commit e620d45065c7b5b8d6ae11217c09c09380103b83
# Author: Breno Leitao <leitao@debian.org>
# Date:   Wed Jan 16 14:47:44 2019 -0200
# 
#     powerpc/tm: Avoid machine crash on rt_sigreturn()
#     
#     There is a kernel crash that happens if rt_sigreturn() is called inside
#     a transactional block.
#     
#     This crash happens if the kernel hits an in-kernel page fault when
#     accessing userspace memory, usually through copy_ckvsx_to_user(). A
#     major page fault calls might_sleep() function, which can cause a task
#     reschedule. A task reschedule (switch_to()) reclaim and recheckpoint
#     the TM states, but, in the signal return path, the checkpointed memory
#     was already reclaimed, thus the exception stack has MSR that points to
#     MSR[TS]=0.
#     
#     When the code returns from might_sleep() and a task reschedule
#     happened, then this task is returned with the memory recheckpointed,
#     and CPU MSR[TS] = suspended.
#     
#     This means that there is a side effect at might_sleep() if it is
#     called with CPU MSR[TS] = 0 and the task has regs->msr[TS] != 0.
#     
#     This side effect can cause a TM bad thing, since at the exception
#     entrance, the stack saves MSR[TS]=0, and this is what will be used at
#     RFID, but, the processor has MSR[TS] = Suspended, and this transition
#     will be invalid and a TM Bad thing will be raised, causing the
#     following crash:
#     
#       Unexpected TM Bad Thing exception at c00000000000e9ec (msr 0x8000000302a03031) tm_scratch=800000010280b033
#       cpu 0xc: Vector: 700 (Program Check) at [c00000003ff1fd70]
#           pc: c00000000000e9ec: fast_exception_return+0x100/0x1bc
#           lr: c000000000032948: handle_rt_signal64+0xb8/0xaf0
#           sp: c0000004263ebc40
#          msr: 8000000302a03031
#         current = 0xc000000415050300
#         paca    = 0xc00000003ffc4080         irqmask: 0x03   irq_happened: 0x01
#           pid   = 25006, comm = sigfuz
#       Linux version 5.0.0-rc1-00001-g3bd6e94bec12 (breno@debian) (gcc version 8.2.0 (Debian 8.2.0-3)) #899 SMP Mon Jan 7 11:30:07 EST 2019
#       WARNING: exception is not recoverable, can't continue
#       enter ? for help
#       [c0000004263ebc40] c000000000032948 handle_rt_signal64+0xb8/0xaf0 (unreliable)
#       [c0000004263ebd30] c000000000022780 do_notify_resume+0x2f0/0x430
#       [c0000004263ebe20] c00000000000e844 ret_from_except_lite+0x70/0x74
#       --- Exception: c00 (System Call) at 00007fffbaac400c
#       SP (7fffeca90f40) is in userspace
#     
#     The solution for this problem is running the sigreturn code with
#     regs->msr[TS] disabled, thus, avoiding hitting the side effect above.
#     This does not seem to be a problem since regs->msr will be replaced by
#     the ucontext value, so, it is being flushed already. In this case, it
#     is flushed earlier.
#     
#     Signed-off-by: Breno Leitao <leitao@debian.org>
#     Acked-by: Michael Neuling <mikey@neuling.org>
#     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 e620d45065c7b5b8d6ae11217c09c09380103b83
# < make -s -j 80 ARCH=powerpc O=/kisskb/build/powerpc-next_85xx_mpc8560_ads_defconfig_powerpc-gcc5 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-5.5.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  85xx/mpc8560_ads_defconfig
# make -s -j 80 ARCH=powerpc O=/kisskb/build/powerpc-next_85xx_mpc8560_ads_defconfig_powerpc-gcc5 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-5.5.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  
<stdin>:1478:2: warning: #warning syscall pidfd_send_signal not implemented [-Wcpp]
<stdin>:1481:2: warning: #warning syscall io_uring_setup not implemented [-Wcpp]
<stdin>:1484:2: warning: #warning syscall io_uring_enter not implemented [-Wcpp]
<stdin>:1487:2: warning: #warning syscall io_uring_register not implemented [-Wcpp]
INFO: Uncompressed kernel (size 0x4f44e4) overlaps the address of the wrapper(0x400000)
INFO: Fixing the link_address of wrapper to (0x500000)
INFO: Uncompressed kernel (size 0x4e3dbc) overlaps the address of the wrapper(0x400000)
INFO: Fixing the link_address of wrapper to (0x500000)
Image Name:   Linux-5.1.0-rc3-ge620d45065c7
Created:      Thu May  2 01:19:25 2019
Image Type:   PowerPC Linux Kernel Image (gzip compressed)
Data Size:    2561341 Bytes = 2501.31 KiB = 2.44 MiB
Load Address: 00000000
Entry Point:  00000000
Image Name:   Linux-5.1.0-rc3-ge620d45065c7
Created:      Thu May  2 01:19:25 2019
Image Type:   PowerPC Linux Kernel Image (gzip compressed)
Data Size:    2591465 Bytes = 2530.73 KiB = 2.47 MiB
Load Address: 00500000
Entry Point:  00500314
Completed OK
# rm -rf /kisskb/build/powerpc-next_85xx_mpc8560_ads_defconfig_powerpc-gcc5
# Build took: 0:00:44.139378