livepatch/s390: add TIF_PATCH_PENDING thread flag

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>
Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

diff --git a/arch/s390/include/asm/thread_info.h b/arch/s390/include/asm/thread_info.h
index 4977668..646845e 100644 (file)
--- a/arch/s390/include/asm/thread_info.h
+++ b/arch/s390/include/asm/thread_info.h
@@ -56,6 +56,7 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src);
 #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 */
@@ -74,6 +75,7 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src);
 #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 dff2152..a08b5ee 100644 (file)
--- a/arch/s390/kernel/entry.S
+++ b/arch/s390/kernel/entry.S
@@ -47,7 +47,7 @@ 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_PRIMARY | \
@@ -334,6 +334,11 @@ 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
@@ -409,6 +414,16 @@ ENTRY(system_call)
 #endif
 
 #
+# _TIF_PATCH_PENDING is set, call klp_update_patch_state
+#
+#ifdef CONFIG_LIVEPATCH
+.Lsysc_patch_pending:
+       lg      %r2,__LC_CURRENT        # pass pointer to task struct
+       larl    %r14,.Lsysc_return
+       jg      klp_update_patch_state
+#endif
+
+#
 # _PIF_PER_TRAP is set, call do_per_trap
 #
 .Lsysc_singlestep:
@@ -659,6 +674,10 @@ 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
@@ -708,6 +727,16 @@ ENTRY(io_int_handler)
        j       .Lio_return
 
 #
+# _TIF_PATCH_PENDING is set, call klp_update_patch_state
+#
+#ifdef CONFIG_LIVEPATCH
+.Lio_patch_pending:
+       lg      %r2,__LC_CURRENT        # pass pointer to task struct
+       larl    %r14,.Lio_return
+       jg      klp_update_patch_state
+#endif
+
+#
 # _TIF_SIGPENDING or is set, call do_signal
 #
 .Lio_sigpending: