x86/entry/32: Convert IRET exception to IDTENTRY_SW

Convert the IRET exception handler to IDTENTRY_SW. This is slightly
different than the conversions of hardware exceptions as the IRET exception
is invoked via an exception table when IRET faults. So it just uses the
IDTENTRY_SW mechanism for consistency. It does not emit ASM code as it does
not fit the other idtentry exceptions.

  - Implement the C entry point with DEFINE_IDTENTRY_SW() which maps to
    DEFINE_IDTENTRY()
  - Fixup the XEN/PV code
  - Remove the old prototypes
  - Remove the RCU warning as the new entry macro ensures correctness

No functional change.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Andy Lutomirski <luto@kernel.org>
Link: https://lkml.kernel.org/r/20200505134906.128769226@linutronix.de

arch/x86/entry/entry_32.S

@@ -1147,9 +1147,9 @@ restore_all_kernel:
 	jmp	.Lirq_return
 
 .section .fixup, "ax"
-SYM_CODE_START(iret_exc)
+SYM_CODE_START(asm_iret_error)
 	pushl	$0				# no error code
-	pushl	$do_iret_error
+	pushl	$iret_error
 
 #ifdef CONFIG_DEBUG_ENTRY
 	/*
@@ -1163,10 +1163,10 @@ SYM_CODE_START(iret_exc)
 	popl	%eax
 #endif
 
-	jmp	common_exception
-SYM_CODE_END(iret_exc)
+	jmp	handle_exception
+SYM_CODE_END(asm_iret_error)
 .previous
-	_ASM_EXTABLE(.Lirq_return, iret_exc)
+	_ASM_EXTABLE(.Lirq_return, asm_iret_error)
 SYM_FUNC_END(entry_INT80_32)
 
 .macro FIXUP_ESPFIX_STACK
@@ -1293,7 +1293,7 @@ SYM_FUNC_END(name)
 #ifdef CONFIG_PARAVIRT
 SYM_CODE_START(native_iret)
 	iret
-	_ASM_EXTABLE(native_iret, iret_exc)
+	_ASM_EXTABLE(native_iret, asm_iret_error)
 SYM_CODE_END(native_iret)
 #endif
 
@@ -1358,7 +1358,7 @@ SYM_FUNC_START(xen_failsafe_callback)
 	popl	%eax
 	lea	16(%esp), %esp
 	jz	5f
-	jmp	iret_exc
+	jmp	asm_iret_error
 5:	pushl	$-1				/* orig_ax = -1 => not a system call */
 	SAVE_ALL
 	ENCODE_FRAME_POINTER

arch/x86/include/asm/idtentry.h

@@ -57,6 +57,10 @@ __visible noinstr void func(struct pt_regs *regs)			\
 									\
 static __always_inline void __##func(struct pt_regs *regs)
 
+/* Special case for 32bit IRET 'trap' */
+#define DECLARE_IDTENTRY_SW	DECLARE_IDTENTRY
+#define DEFINE_IDTENTRY_SW	DEFINE_IDTENTRY
+
 /**
  * DECLARE_IDTENTRY_ERRORCODE - Declare functions for simple IDT entry points
  *				Error code pushed by hardware
@@ -111,6 +115,9 @@ static __always_inline void __##func(struct pt_regs *regs,		\
 #define DECLARE_IDTENTRY_ERRORCODE(vector, func)			\
 	idtentry vector asm_##func func has_error_code=1 sane=1
 
+/* Special case for 32bit IRET 'trap'. Do not emit ASM code */
+#define DECLARE_IDTENTRY_SW(vector, func)
+
 #endif /* __ASSEMBLY__ */
 
 /*
@@ -133,6 +140,9 @@ DECLARE_IDTENTRY(X86_TRAP_SPURIOUS,	exc_spurious_interrupt_bug);
 DECLARE_IDTENTRY(X86_TRAP_MF,		exc_coprocessor_error);
 DECLARE_IDTENTRY(X86_TRAP_XF,		exc_simd_coprocessor_error);
 
+/* 32bit software IRET trap. Do not emit ASM code */
+DECLARE_IDTENTRY_SW(X86_TRAP_IRET,	iret_error);
+
 /* Simple exception entries with error code pushed by hardware */
 DECLARE_IDTENTRY_ERRORCODE(X86_TRAP_TS,	exc_invalid_tss);
 DECLARE_IDTENTRY_ERRORCODE(X86_TRAP_NP,	exc_segment_not_present);

arch/x86/include/asm/traps.h

@@ -39,9 +39,6 @@ dotraplinkage void do_nmi(struct pt_regs *regs, long error_code);
 dotraplinkage void do_int3(struct pt_regs *regs, long error_code);
 dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code, unsigned long cr2);
 dotraplinkage void do_page_fault(struct pt_regs *regs, unsigned long error_code, unsigned long address);
-#ifdef CONFIG_X86_32
-dotraplinkage void do_iret_error(struct pt_regs *regs, long error_code);
-#endif
 dotraplinkage void do_mce(struct pt_regs *regs, long error_code);
 
 #ifdef CONFIG_X86_64

arch/x86/kernel/traps.c

@@ -925,14 +925,12 @@ DEFINE_IDTENTRY(exc_device_not_available)
 }
 
 #ifdef CONFIG_X86_32
-dotraplinkage void do_iret_error(struct pt_regs *regs, long error_code)
+DEFINE_IDTENTRY_SW(iret_error)
 {
-	RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
 	local_irq_enable();
-
-	if (notify_die(DIE_TRAP, "iret exception", regs, error_code,
+	if (notify_die(DIE_TRAP, "iret exception", regs, 0,
 			X86_TRAP_IRET, SIGILL) != NOTIFY_STOP) {
-		do_trap(X86_TRAP_IRET, SIGILL, "iret exception", regs, error_code,
+		do_trap(X86_TRAP_IRET, SIGILL, "iret exception", regs, 0,
 			ILL_BADSTK, (void __user *)NULL);
 	}
 	local_irq_disable();

arch/x86/xen/xen-asm_32.S

@@ -117,7 +117,7 @@ iret_restore_end:
 
 1:	iret
 xen_iret_end_crit:
-	_ASM_EXTABLE(1b, iret_exc)
+	_ASM_EXTABLE(1b, asm_iret_error)
 
 hyper_iret:
 	/* put this out of line since its very rarely used */