uprobes/x86: Add is_64bit_mm(), kill validate_insn_bits()

1. Extract the ->ia32_compat check from 64bit validate_insn_bits()
   into the new helper, is_64bit_mm(), it will have more users.

   TODO: this checks is actually wrong if mm owner is X32 task,
   we need another fix which changes set_personality_ia32().

   TODO: even worse, the whole 64-or-32-bit logic is very broken
   and the fix is not simple, we need the nontrivial changes in
   the core uprobes code.

2. Kill validate_insn_bits() and change its single caller to use
   uprobe_init_insn(is_64bit_mm(mm).
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Jim Keniston <jkenisto@us.ibm.com>
Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>

arch/x86/kernel/uprobes.c

@@ -231,6 +231,11 @@ static int uprobe_init_insn(struct arch_uprobe *auprobe, struct insn *insn, bool
 }
 
 #ifdef CONFIG_X86_64
+static inline bool is_64bit_mm(struct mm_struct *mm)
+{
+	return	!config_enabled(CONFIG_IA32_EMULATION) ||
+		!mm->context.ia32_compat;
+}
 /*
  * If arch_uprobe->insn doesn't use rip-relative addressing, return
  * immediately.  Otherwise, rewrite the instruction so that it accesses
@@ -355,13 +360,11 @@ handle_riprel_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs, long *
 			*correction += 4;
 	}
 }
-
-static int validate_insn_bits(struct arch_uprobe *auprobe, struct mm_struct *mm, struct insn *insn)
+#else /* 32-bit: */
+static inline bool is_64bit_mm(struct mm_struct *mm)
 {
-	bool x86_64 = !mm->context.ia32_compat;
-	return uprobe_init_insn(auprobe, insn, x86_64);
+	return false;
 }
-#else /* 32-bit: */
 /*
  * No RIP-relative addressing on 32-bit
  */
@@ -376,11 +379,6 @@ static void handle_riprel_post_xol(struct arch_uprobe *auprobe, struct pt_regs *
 					long *correction)
 {
 }
-
-static int validate_insn_bits(struct arch_uprobe *auprobe, struct mm_struct *mm,  struct insn *insn)
-{
-	return uprobe_init_insn(auprobe, insn, false);
-}
 #endif /* CONFIG_X86_64 */
 
 struct uprobe_xol_ops {
@@ -625,7 +623,7 @@ int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe, struct mm_struct *mm,
 	bool fix_ip = true, fix_call = false;
 	int ret;
 
-	ret = validate_insn_bits(auprobe, mm, &insn);
+	ret = uprobe_init_insn(auprobe, &insn, is_64bit_mm(mm));
 	if (ret)
 		return ret;