Two fixes for the x86 interrupt code:

- Unbreak the magic 'search the timer interrupt' logic in IO/APIC code
     which got wreckaged when the core interrupt code made the state
     tracking logic stricter. That caused the interrupt line to stay masked
     after switching from IO/APIC to PIC delivery mode, which obviously
     prevents interrupts from being delivered.
 
   - Make run_on_irqstack_code() typesafe. The function argument is a void
     pointer which is then casted to 'void (*fun)(void *). This breaks
     Control Flow Integrity checking in clang. Use proper helper functions
     for the three variants reuqired.
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Merge tag 'x86-urgent-2020-09-27' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 fixes from Thomas Gleixner:
 "Two fixes for the x86 interrupt code:

   - Unbreak the magic 'search the timer interrupt' logic in IO/APIC
     code which got wreckaged when the core interrupt code made the
     state tracking logic stricter.

     That caused the interrupt line to stay masked after switching from
     IO/APIC to PIC delivery mode, which obviously prevents interrupts
     from being delivered.

   - Make run_on_irqstack_code() typesafe. The function argument is a
     void pointer which is then cast to 'void (*fun)(void *).

     This breaks Control Flow Integrity checking in clang. Use proper
     helper functions for the three variants reuqired"

* tag 'x86-urgent-2020-09-27' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/ioapic: Unbreak check_timer()
  x86/irq: Make run_on_irqstack_cond() typesafe

arch/x86/entry/common.c

@@ -299,7 +299,7 @@ __visible noinstr void xen_pv_evtchn_do_upcall(struct pt_regs *regs)
 	old_regs = set_irq_regs(regs);
 
 	instrumentation_begin();
-	run_on_irqstack_cond(__xen_pv_evtchn_do_upcall, NULL, regs);
+	run_on_irqstack_cond(__xen_pv_evtchn_do_upcall, regs);
 	instrumentation_begin();
 
 	set_irq_regs(old_regs);

arch/x86/entry/entry_64.S

@@ -682,6 +682,8 @@ SYM_CODE_END(.Lbad_gs)
  * rdx: Function argument (can be NULL if none)
  */
 SYM_FUNC_START(asm_call_on_stack)
+SYM_INNER_LABEL(asm_call_sysvec_on_stack, SYM_L_GLOBAL)
+SYM_INNER_LABEL(asm_call_irq_on_stack, SYM_L_GLOBAL)
 	/*
 	 * Save the frame pointer unconditionally. This allows the ORC
 	 * unwinder to handle the stack switch.

arch/x86/include/asm/idtentry.h

@@ -242,7 +242,7 @@ __visible noinstr void func(struct pt_regs *regs)			\
 	instrumentation_begin();					\
 	irq_enter_rcu();						\
 	kvm_set_cpu_l1tf_flush_l1d();					\
-	run_on_irqstack_cond(__##func, regs, regs);			\
+	run_sysvec_on_irqstack_cond(__##func, regs);			\
 	irq_exit_rcu();							\
 	instrumentation_end();						\
 	irqentry_exit(regs, state);					\

arch/x86/include/asm/irq_stack.h

@@ -12,20 +12,50 @@ static __always_inline bool irqstack_active(void)
 	return __this_cpu_read(irq_count) != -1;
 }
 
-void asm_call_on_stack(void *sp, void *func, void *arg);
+void asm_call_on_stack(void *sp, void (*func)(void), void *arg);
+void asm_call_sysvec_on_stack(void *sp, void (*func)(struct pt_regs *regs),
+			      struct pt_regs *regs);
+void asm_call_irq_on_stack(void *sp, void (*func)(struct irq_desc *desc),
+			   struct irq_desc *desc);
 
-static __always_inline void __run_on_irqstack(void *func, void *arg)
+static __always_inline void __run_on_irqstack(void (*func)(void))
 {
 	void *tos = __this_cpu_read(hardirq_stack_ptr);
 
 	__this_cpu_add(irq_count, 1);
-	asm_call_on_stack(tos - 8, func, arg);
+	asm_call_on_stack(tos - 8, func, NULL);
+	__this_cpu_sub(irq_count, 1);
+}
+
+static __always_inline void
+__run_sysvec_on_irqstack(void (*func)(struct pt_regs *regs),
+			 struct pt_regs *regs)
+{
+	void *tos = __this_cpu_read(hardirq_stack_ptr);
+
+	__this_cpu_add(irq_count, 1);
+	asm_call_sysvec_on_stack(tos - 8, func, regs);
+	__this_cpu_sub(irq_count, 1);
+}
+
+static __always_inline void
+__run_irq_on_irqstack(void (*func)(struct irq_desc *desc),
+		      struct irq_desc *desc)
+{
+	void *tos = __this_cpu_read(hardirq_stack_ptr);
+
+	__this_cpu_add(irq_count, 1);
+	asm_call_irq_on_stack(tos - 8, func, desc);
 	__this_cpu_sub(irq_count, 1);
 }
 
 #else /* CONFIG_X86_64 */
 static inline bool irqstack_active(void) { return false; }
-static inline void __run_on_irqstack(void *func, void *arg) { }
+static inline void __run_on_irqstack(void (*func)(void)) { }
+static inline void __run_sysvec_on_irqstack(void (*func)(struct pt_regs *regs),
+					    struct pt_regs *regs) { }
+static inline void __run_irq_on_irqstack(void (*func)(struct irq_desc *desc),
+					 struct irq_desc *desc) { }
 #endif /* !CONFIG_X86_64 */
 
 static __always_inline bool irq_needs_irq_stack(struct pt_regs *regs)
@@ -37,17 +67,40 @@ static __always_inline bool irq_needs_irq_stack(struct pt_regs *regs)
 	return !user_mode(regs) && !irqstack_active();
 }
 
-static __always_inline void run_on_irqstack_cond(void *func, void *arg,
+
+static __always_inline void run_on_irqstack_cond(void (*func)(void),
 						 struct pt_regs *regs)
 {
-	void (*__func)(void *arg) = func;
-
 	lockdep_assert_irqs_disabled();
 
 	if (irq_needs_irq_stack(regs))
-		__run_on_irqstack(__func, arg);
+		__run_on_irqstack(func);
 	else
-		__func(arg);
+		func();
+}
+
+static __always_inline void
+run_sysvec_on_irqstack_cond(void (*func)(struct pt_regs *regs),
+			    struct pt_regs *regs)
+{
+	lockdep_assert_irqs_disabled();
+
+	if (irq_needs_irq_stack(regs))
+		__run_sysvec_on_irqstack(func, regs);
+	else
+		func(regs);
+}
+
+static __always_inline void
+run_irq_on_irqstack_cond(void (*func)(struct irq_desc *desc), struct irq_desc *desc,
+			 struct pt_regs *regs)
+{
+	lockdep_assert_irqs_disabled();
+
+	if (irq_needs_irq_stack(regs))
+		__run_irq_on_irqstack(func, desc);
+	else
+		func(desc);
 }
 
 #endif

arch/x86/kernel/apic/io_apic.c

@@ -2243,6 +2243,7 @@ static inline void __init check_timer(void)
 	legacy_pic->init(0);
 	legacy_pic->make_irq(0);
 	apic_write(APIC_LVT0, APIC_DM_EXTINT);
+	legacy_pic->unmask(0);
 
 	unlock_ExtINT_logic();
 

arch/x86/kernel/irq.c

@@ -227,7 +227,7 @@ static __always_inline void handle_irq(struct irq_desc *desc,
 				       struct pt_regs *regs)
 {
 	if (IS_ENABLED(CONFIG_X86_64))
-		run_on_irqstack_cond(desc->handle_irq, desc, regs);
+		run_irq_on_irqstack_cond(desc->handle_irq, desc, regs);
 	else
 		__handle_irq(desc, regs);
 }

arch/x86/kernel/irq_64.c

@@ -74,5 +74,5 @@ int irq_init_percpu_irqstack(unsigned int cpu)
 
 void do_softirq_own_stack(void)
 {
-	run_on_irqstack_cond(__do_softirq, NULL, NULL);
+	run_on_irqstack_cond(__do_softirq, NULL);
 }