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Subject[PATCH 3.16 073/136] s390: fix transactional execution control register handling
3.16.54-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Heiko Carstens <heiko.carstens@de.ibm.com>

commit a1c5befc1c24eb9c1ee83f711e0f21ee79cbb556 upstream.

Dan Horák reported the following crash related to transactional execution:

User process fault: interruption code 0013 ilc:3 in libpthread-2.26.so[3ff93c00000+1b000]
CPU: 2 PID: 1 Comm: /init Not tainted 4.13.4-300.fc27.s390x #1
Hardware name: IBM 2827 H43 400 (z/VM 6.4.0)
task: 00000000fafc8000 task.stack: 00000000fafc4000
User PSW : 0705200180000000 000003ff93c14e70
R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:1 AS:0 CC:2 PM:0 RI:0 EA:3
User GPRS: 0000000000000077 000003ff00000000 000003ff93144d48 000003ff93144d5e
0000000000000000 0000000000000002 0000000000000000 000003ff00000000
0000000000000000 0000000000000418 0000000000000000 000003ffcc9fe770
000003ff93d28f50 000003ff9310acf0 000003ff92b0319a 000003ffcc9fe6d0
User Code: 000003ff93c14e62: 60e0b030 std %f14,48(%r11)
000003ff93c14e66: 60f0b038 std %f15,56(%r11)
#000003ff93c14e6a: e5600000ff0e tbegin 0,65294
>000003ff93c14e70: a7740006 brc 7,3ff93c14e7c
000003ff93c14e74: a7080000 lhi %r0,0
000003ff93c14e78: a7f40023 brc 15,3ff93c14ebe
000003ff93c14e7c: b2220000 ipm %r0
000003ff93c14e80: 8800001c srl %r0,28

There are several bugs with control register handling with respect to
transactional execution:

- on task switch update_per_regs() is only called if the next task has
an mm (is not a kernel thread). This however is incorrect. This
breaks e.g. for user mode helper handling, where the kernel creates
a kernel thread and then execve's a user space program. Control
register contents related to transactional execution won't be
updated on execve. If the previous task ran with transactional
execution disabled then the new task will also run with
transactional execution disabled, which is incorrect. Therefore call
update_per_regs() unconditionally within switch_to().

- on startup the transactional execution facility is not enabled for
the idle thread. This is not really a bug, but an inconsistency to
other facilities. Therefore enable the facility if it is available.

- on fork the new thread's per_flags field is not cleared. This means
that a child process inherits the PER_FLAG_NO_TE flag. This flag can
be set with a ptrace request to disable transactional execution for
the current process. It should not be inherited by new child
processes in order to be consistent with the handling of all other
PER related debugging options. Therefore clear the per_flags field in
copy_thread_tls().

Reported-and-tested-by: Dan Horák <dan@danny.cz>
Fixes: d35339a42dd1 ("s390: add support for transactional memory")
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
arch/s390/include/asm/switch_to.h | 2 +-
arch/s390/kernel/early.c | 4 +++-
arch/s390/kernel/process.c | 1 +
3 files changed, 5 insertions(+), 2 deletions(-)

--- a/arch/s390/include/asm/switch_to.h
+++ b/arch/s390/include/asm/switch_to.h
@@ -124,12 +124,12 @@ static inline void restore_access_regs(u
save_access_regs(&prev->thread.acrs[0]); \
save_ri_cb(prev->thread.ri_cb); \
} \
+ update_cr_regs(next); \
if (next->mm) { \
restore_fp_ctl(&next->thread.fp_regs.fpc); \
restore_fp_regs(next->thread.fp_regs.fprs); \
restore_access_regs(&next->thread.acrs[0]); \
restore_ri_cb(next->thread.ri_cb, prev->thread.ri_cb); \
- update_cr_regs(next); \
} \
prev = __switch_to(prev,next); \
} while (0)
--- a/arch/s390/kernel/early.c
+++ b/arch/s390/kernel/early.c
@@ -388,8 +388,10 @@ static __init void detect_machine_facili
S390_lowcore.machine_flags |= MACHINE_FLAG_IDTE;
if (test_facility(40))
S390_lowcore.machine_flags |= MACHINE_FLAG_LPP;
- if (test_facility(50) && test_facility(73))
+ if (test_facility(50) && test_facility(73)) {
S390_lowcore.machine_flags |= MACHINE_FLAG_TE;
+ __ctl_set_bit(0, 55);
+ }
if (test_facility(66))
S390_lowcore.machine_flags |= MACHINE_FLAG_RRBM;
if (test_facility(51))
--- a/arch/s390/kernel/process.c
+++ b/arch/s390/kernel/process.c
@@ -123,6 +123,7 @@ int copy_thread(unsigned long clone_flag
memset(&p->thread.per_user, 0, sizeof(p->thread.per_user));
memset(&p->thread.per_event, 0, sizeof(p->thread.per_event));
clear_tsk_thread_flag(p, TIF_SINGLE_STEP);
+ p->thread.per_flags = 0;
/* Initialize per thread user and system timer values */
ti = task_thread_info(p);
ti->user_timer = 0;
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