Merge branch 'x86-asm-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 asm changes from Ingo Molnar:
 "The main changes in this cycle were the x86/entry and sysret
  enhancements from Andy Lutomirski, see merge commits 772a9aca125 and
  b57c0b5175dd for details"

[ Exectutive summary: IST exceptions that interrupt user space will run
  on the regular kernel stack instead of the IST stack.  Which
  simplifies things particularly on return to user space.

  The sysret cleanup ends up simplifying the logic on when we can use
  sysret vs when we have to use iret.                - Linus ]

* 'x86-asm-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86_64, entry: Remove the syscall exit audit and schedule optimizations
  x86_64, entry: Use sysret to return to userspace when possible
  x86, traps: Fix ist_enter from userspace
  x86, vdso: teach 'make clean' remove vdso64 binaries
  x86_64 entry: Fix RCX for ptraced syscalls
  x86: entry_64.S: fold SAVE_ARGS_IRQ macro into its sole user
  x86: ia32entry.S: fix wrong symbolic constant usage: R11->ARGOFFSET
  x86: entry_64.S: delete unused code
  x86, mce: Get rid of TIF_MCE_NOTIFY and associated mce tricks
  x86, traps: Add ist_begin_non_atomic and ist_end_non_atomic
  x86: Clean up current_stack_pointer
  x86, traps: Track entry into and exit from IST context
  x86, entry: Switch stacks on a paranoid entry from userspace

1 files changed, 95 insertions, 24 deletions

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 88900e288021..c74f2f5652da 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -108,6 +108,88 @@ static inline void preempt_conditional_cli(struct pt_regs *regs)
 	preempt_count_dec();
 }
 
+enum ctx_state ist_enter(struct pt_regs *regs)
+{
+	enum ctx_state prev_state;
+
+	if (user_mode_vm(regs)) {
+		/* Other than that, we're just an exception. */
+		prev_state = exception_enter();
+	} else {
+		/*
+		 * We might have interrupted pretty much anything.  In
+		 * fact, if we're a machine check, we can even interrupt
+		 * NMI processing.  We don't want in_nmi() to return true,
+		 * but we need to notify RCU.
+		 */
+		rcu_nmi_enter();
+		prev_state = IN_KERNEL;  /* the value is irrelevant. */
+	}
+
+	/*
+	 * We are atomic because we're on the IST stack (or we're on x86_32,
+	 * in which case we still shouldn't schedule).
+	 *
+	 * This must be after exception_enter(), because exception_enter()
+	 * won't do anything if in_interrupt() returns true.
+	 */
+	preempt_count_add(HARDIRQ_OFFSET);
+
+	/* This code is a bit fragile.  Test it. */
+	rcu_lockdep_assert(rcu_is_watching(), "ist_enter didn't work");
+
+	return prev_state;
+}
+
+void ist_exit(struct pt_regs *regs, enum ctx_state prev_state)
+{
+	/* Must be before exception_exit. */
+	preempt_count_sub(HARDIRQ_OFFSET);
+
+	if (user_mode_vm(regs))
+		return exception_exit(prev_state);
+	else
+		rcu_nmi_exit();
+}
+
+/**
+ * ist_begin_non_atomic() - begin a non-atomic section in an IST exception
+ * @regs:	regs passed to the IST exception handler
+ *
+ * IST exception handlers normally cannot schedule.  As a special
+ * exception, if the exception interrupted userspace code (i.e.
+ * user_mode_vm(regs) would return true) and the exception was not
+ * a double fault, it can be safe to schedule.  ist_begin_non_atomic()
+ * begins a non-atomic section within an ist_enter()/ist_exit() region.
+ * Callers are responsible for enabling interrupts themselves inside
+ * the non-atomic section, and callers must call is_end_non_atomic()
+ * before ist_exit().
+ */
+void ist_begin_non_atomic(struct pt_regs *regs)
+{
+	BUG_ON(!user_mode_vm(regs));
+
+	/*
+	 * Sanity check: we need to be on the normal thread stack.  This
+	 * will catch asm bugs and any attempt to use ist_preempt_enable
+	 * from double_fault.
+	 */
+	BUG_ON(((current_stack_pointer() ^ this_cpu_read_stable(kernel_stack))
+		& ~(THREAD_SIZE - 1)) != 0);
+
+	preempt_count_sub(HARDIRQ_OFFSET);
+}
+
+/**
+ * ist_end_non_atomic() - begin a non-atomic section in an IST exception
+ *
+ * Ends a non-atomic section started with ist_begin_non_atomic().
+ */
+void ist_end_non_atomic(void)
+{
+	preempt_count_add(HARDIRQ_OFFSET);
+}
+
 static nokprobe_inline int
 do_trap_no_signal(struct task_struct *tsk, int trapnr, char *str,
 		  struct pt_regs *regs,	long error_code)
@@ -251,6 +333,8 @@ dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code)
 	 * end up promoting it to a doublefault.  In that case, modify
 	 * the stack to make it look like we just entered the #GP
 	 * handler from user space, similar to bad_iret.
+	 *
+	 * No need for ist_enter here because we don't use RCU.
 	 */
 	if (((long)regs->sp >> PGDIR_SHIFT) == ESPFIX_PGD_ENTRY &&
 		regs->cs == __KERNEL_CS &&
@@ -263,12 +347,12 @@ dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code)
 		normal_regs->orig_ax = 0;  /* Missing (lost) #GP error code */
 		regs->ip = (unsigned long)general_protection;
 		regs->sp = (unsigned long)&normal_regs->orig_ax;
+
 		return;
 	}
 #endif
 
-	exception_enter();
-	/* Return not checked because double check cannot be ignored */
+	ist_enter(regs);  /* Discard prev_state because we won't return. */
 	notify_die(DIE_TRAP, str, regs, error_code, X86_TRAP_DF, SIGSEGV);
 
 	tsk->thread.error_code = error_code;
@@ -434,7 +518,7 @@ dotraplinkage void notrace do_int3(struct pt_regs *regs, long error_code)
 	if (poke_int3_handler(regs))
 		return;
 
-	prev_state = exception_enter();
+	prev_state = ist_enter(regs);
 #ifdef CONFIG_KGDB_LOW_LEVEL_TRAP
 	if (kgdb_ll_trap(DIE_INT3, "int3", regs, error_code, X86_TRAP_BP,
 				SIGTRAP) == NOTIFY_STOP)
@@ -460,33 +544,20 @@ dotraplinkage void notrace do_int3(struct pt_regs *regs, long error_code)
 	preempt_conditional_cli(regs);
 	debug_stack_usage_dec();
 exit:
-	exception_exit(prev_state);
+	ist_exit(regs, prev_state);
 }
 NOKPROBE_SYMBOL(do_int3);
 
 #ifdef CONFIG_X86_64
 /*
- * Help handler running on IST stack to switch back to user stack
- * for scheduling or signal handling. The actual stack switch is done in
- * entry.S
+ * Help handler running on IST stack to switch off the IST stack if the
+ * interrupted code was in user mode. The actual stack switch is done in
+ * entry_64.S
  */
 asmlinkage __visible notrace struct pt_regs *sync_regs(struct pt_regs *eregs)
 {
-	struct pt_regs *regs = eregs;
-	/* Did already sync */
-	if (eregs == (struct pt_regs *)eregs->sp)
-		;
-	/* Exception from user space */
-	else if (user_mode(eregs))
-		regs = task_pt_regs(current);
-	/*
-	 * Exception from kernel and interrupts are enabled. Move to
-	 * kernel process stack.
-	 */
-	else if (eregs->flags & X86_EFLAGS_IF)
-		regs = (struct pt_regs *)(eregs->sp -= sizeof(struct pt_regs));
-	if (eregs != regs)
-		*regs = *eregs;
+	struct pt_regs *regs = task_pt_regs(current);
+	*regs = *eregs;
 	return regs;
 }
 NOKPROBE_SYMBOL(sync_regs);
@@ -554,7 +625,7 @@ dotraplinkage void do_debug(struct pt_regs *regs, long error_code)
 	unsigned long dr6;
 	int si_code;
 
-	prev_state = exception_enter();
+	prev_state = ist_enter(regs);
 
 	get_debugreg(dr6, 6);
 
@@ -629,7 +700,7 @@ dotraplinkage void do_debug(struct pt_regs *regs, long error_code)
 	debug_stack_usage_dec();
 
 exit:
-	exception_exit(prev_state);
+	ist_exit(regs, prev_state);
 }
 NOKPROBE_SYMBOL(do_debug);