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Subject[RFC PATCH v2 12/18] livepatch/s390: add TIF_PATCH_PENDING thread flag
Date
From: Miroslav Benes <mbenes@suse.cz>

Update a task's patch state when returning from a system call or user
space interrupt, or after handling a signal.

This greatly increases the chances of a patch operation succeeding. If
a task is I/O bound, it can be patched when returning from a system
call. If a task is CPU bound, it can be patched when returning from an
interrupt. If a task is sleeping on a to-be-patched function, the user
can send SIGSTOP and SIGCONT to force it to switch.

Since there are two ways the syscall can be restarted on return from a
signal handling process, it is important to clear the flag before
do_signal() is called. Otherwise we could miss the migration if we used
SIGSTOP/SIGCONT procedure or fake signal to migrate patching blocking
tasks. If we place our hook to sysc_work label in entry before
TIF_SIGPENDING is evaluated we kill two birds with one stone. The task
is correctly migrated in all return paths from a syscall.

Signed-off-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
arch/s390/include/asm/thread_info.h | 2 ++
arch/s390/kernel/entry.S | 31 ++++++++++++++++++++++++++++++-
2 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/arch/s390/include/asm/thread_info.h b/arch/s390/include/asm/thread_info.h
index 8642c1d..b69d538 100644
--- a/arch/s390/include/asm/thread_info.h
+++ b/arch/s390/include/asm/thread_info.h
@@ -75,6 +75,7 @@ void arch_release_task_struct(struct task_struct *tsk);
#define TIF_SIGPENDING 1 /* signal pending */
#define TIF_NEED_RESCHED 2 /* rescheduling necessary */
#define TIF_UPROBE 3 /* breakpointed or single-stepping */
+#define TIF_PATCH_PENDING 4 /* pending live patching update */

#define TIF_31BIT 16 /* 32bit process */
#define TIF_MEMDIE 17 /* is terminating due to OOM killer */
@@ -93,6 +94,7 @@ void arch_release_task_struct(struct task_struct *tsk);
#define _TIF_SIGPENDING _BITUL(TIF_SIGPENDING)
#define _TIF_NEED_RESCHED _BITUL(TIF_NEED_RESCHED)
#define _TIF_UPROBE _BITUL(TIF_UPROBE)
+#define _TIF_PATCH_PENDING _BITUL(TIF_PATCH_PENDING)

#define _TIF_31BIT _BITUL(TIF_31BIT)
#define _TIF_SINGLE_STEP _BITUL(TIF_SINGLE_STEP)
diff --git a/arch/s390/kernel/entry.S b/arch/s390/kernel/entry.S
index 2d47f9c..5db5959 100644
--- a/arch/s390/kernel/entry.S
+++ b/arch/s390/kernel/entry.S
@@ -46,7 +46,7 @@ STACK_SIZE = 1 << STACK_SHIFT
STACK_INIT = STACK_SIZE - STACK_FRAME_OVERHEAD - __PT_SIZE

_TIF_WORK = (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_NEED_RESCHED | \
- _TIF_UPROBE)
+ _TIF_UPROBE | _TIF_PATCH_PENDING)
_TIF_TRACE = (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | _TIF_SECCOMP | \
_TIF_SYSCALL_TRACEPOINT)
_CIF_WORK = (_CIF_MCCK_PENDING | _CIF_ASCE | _CIF_FPU)
@@ -329,6 +329,11 @@ ENTRY(system_call)
#endif
TSTMSK __PT_FLAGS(%r11),_PIF_PER_TRAP
jo .Lsysc_singlestep
+#ifdef CONFIG_LIVEPATCH
+ TSTMSK __TI_flags(%r12),_TIF_PATCH_PENDING
+ jo .Lsysc_patch_pending # handle live patching just before
+ # signals and possible syscall restart
+#endif
TSTMSK __TI_flags(%r12),_TIF_SIGPENDING
jo .Lsysc_sigpending
TSTMSK __TI_flags(%r12),_TIF_NOTIFY_RESUME
@@ -404,6 +409,16 @@ ENTRY(system_call)
#endif

#
+# _TIF_PATCH_PENDING is set, call klp_patch_task
+#
+#ifdef CONFIG_LIVEPATCH
+.Lsysc_patch_pending:
+ lg %r2,__TI_task(%r12)
+ larl %r14,.Lsysc_return
+ jg klp_patch_task
+#endif
+
+#
# _PIF_PER_TRAP is set, call do_per_trap
#
.Lsysc_singlestep:
@@ -652,6 +667,10 @@ ENTRY(io_int_handler)
jo .Lio_mcck_pending
TSTMSK __TI_flags(%r12),_TIF_NEED_RESCHED
jo .Lio_reschedule
+#ifdef CONFIG_LIVEPATCH
+ TSTMSK __TI_flags(%r12),_TIF_PATCH_PENDING
+ jo .Lio_patch_pending
+#endif
TSTMSK __TI_flags(%r12),_TIF_SIGPENDING
jo .Lio_sigpending
TSTMSK __TI_flags(%r12),_TIF_NOTIFY_RESUME
@@ -698,6 +717,16 @@ ENTRY(io_int_handler)
j .Lio_return

#
+# _TIF_PATCH_PENDING is set, call klp_patch_task
+#
+#ifdef CONFIG_LIVEPATCH
+.Lio_patch_pending:
+ lg %r2,__TI_task(%r12)
+ larl %r14,.Lio_return
+ jg klp_patch_task
+#endif
+
+#
# _TIF_SIGPENDING or is set, call do_signal
#
.Lio_sigpending:
--
2.4.11
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