[RFC PATCH for 4.15 05/22] x86: Add support for restartable sequences

Call the rseq_handle_notify_resume() function on return to userspace if
TIF_NOTIFY_RESUME thread flag is set.

Increment the event counter and perform fixup on the pre-signal frame
when a signal is delivered on top of a restartable sequence critical
section.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers-vg+e7yoeK/dWk0Htik3J/w@public.gmane.org>
Reviewed-by: Thomas Gleixner <redacted>
CC: Russell King <linux-lFZ/pmaqli7XmaaqVzeoHQ@public.gmane.org>
CC: Catalin Marinas <redacted>
CC: Will Deacon <redacted>
CC: Paul Turner <redacted>
CC: Andrew Hunter <redacted>
CC: Peter Zijlstra <redacted>
CC: Andy Lutomirski <redacted>
CC: Andi Kleen <andi-Vw/NltI1exuRpAAqCnN02g@public.gmane.org>
CC: Dave Watson <redacted>
CC: Chris Lameter <redacted>
CC: Ingo Molnar <redacted>
CC: "H. Peter Anvin" <redacted>
CC: Ben Maurer <redacted>
CC: Steven Rostedt <redacted>
CC: "Paul E. McKenney" <redacted>
CC: Josh Triplett <redacted>
CC: Linus Torvalds <torvalds-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>
CC: Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>
CC: Boqun Feng <redacted>
CC: linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
---
 arch/x86/Kconfig         | 1 +
 arch/x86/entry/common.c  | 1 +
 arch/x86/kernel/signal.c | 6 ++++++
 3 files changed, 8 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index df3276d6bfe3..4799a440e39c 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig

@@ -174,6 +174,7 @@ config X86
 	select HAVE_REGS_AND_STACK_ACCESS_API
 	select HAVE_RELIABLE_STACKTRACE		if X86_64 && UNWINDER_FRAME_POINTER && STACK_VALIDATION
 	select HAVE_STACK_VALIDATION		if X86_64
+	select HAVE_RSEQ
 	select HAVE_SYSCALL_TRACEPOINTS
 	select HAVE_UNSTABLE_SCHED_CLOCK
 	select HAVE_USER_RETURN_NOTIFIER

diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index d7d3cc24baf4..d65595b201f4 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c

@@ -160,6 +160,7 @@ static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags)
 		if (cached_flags & _TIF_NOTIFY_RESUME) {
 			clear_thread_flag(TIF_NOTIFY_RESUME);
 			tracehook_notify_resume(regs);
+			rseq_handle_notify_resume(regs);
 		}
 
 		if (cached_flags & _TIF_USER_RETURN_NOTIFY)

diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index b9e00e8f1c9b..991017d26d00 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c

@@ -687,6 +687,12 @@ setup_rt_frame(struct ksignal *ksig, struct pt_regs *regs)
 	sigset_t *set = sigmask_to_save();
 	compat_sigset_t *cset = (compat_sigset_t *) set;
 
+	/*
+	 * Increment event counter and perform fixup for the pre-signal
+	 * frame.
+	 */
+	rseq_signal_deliver(regs);
+
 	/* Set up the stack frame */
 	if (is_ia32_frame(ksig)) {
 		if (ksig->ka.sa.sa_flags & SA_SIGINFO)

-- 
2.11.0