x86, mm: fault.c, refactor/simplify the is_prefetch() code

Impact: no functionality changed

Factor out the opcode checker into a helper inline.

The code got a tiny bit smaller:

   text	   data	    bss	    dec	    hex	filename
   4632	     32	     24	   4688	   1250	fault.o.before
   4618	     32	     24	   4674	   1242	fault.o.after

And it got cleaner / easier to review as well.

Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 351d679..72973c7 100644 (file)
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -99,12 +99,58 @@ static inline int notify_page_fault(struct pt_regs *regs)
  *
  * Opcode checker based on code by Richard Brunner.
  */
+static inline int
+check_prefetch_opcode(struct pt_regs *regs, unsigned char *instr,
+                     unsigned char opcode, int *prefetch)
+{
+       unsigned char instr_hi = opcode & 0xf0;
+       unsigned char instr_lo = opcode & 0x0f;
+
+       switch (instr_hi) {
+       case 0x20:
+       case 0x30:
+               /*
+                * Values 0x26,0x2E,0x36,0x3E are valid x86 prefixes.
+                * In X86_64 long mode, the CPU will signal invalid
+                * opcode if some of these prefixes are present so
+                * X86_64 will never get here anyway
+                */
+               return ((instr_lo & 7) == 0x6);
+#ifdef CONFIG_X86_64
+       case 0x40:
+               /*
+                * In AMD64 long mode 0x40..0x4F are valid REX prefixes
+                * Need to figure out under what instruction mode the
+                * instruction was issued. Could check the LDT for lm,
+                * but for now it's good enough to assume that long
+                * mode only uses well known segments or kernel.
+                */
+               return (!user_mode(regs)) || (regs->cs == __USER_CS);
+#endif
+       case 0x60:
+               /* 0x64 thru 0x67 are valid prefixes in all modes. */
+               return (instr_lo & 0xC) == 0x4;
+       case 0xF0:
+               /* 0xF0, 0xF2, 0xF3 are valid prefixes in all modes. */
+               return !instr_lo || (instr_lo>>1) == 1;
+       case 0x00:
+               /* Prefetch instruction is 0x0F0D or 0x0F18 */
+               if (probe_kernel_address(instr, opcode))
+                       return 0;
+
+               *prefetch = (instr_lo == 0xF) &&
+                       (opcode == 0x0D || opcode == 0x18);
+               return 0;
+       default:
+               return 0;
+       }
+}
+
 static int
 is_prefetch(struct pt_regs *regs, unsigned long error_code, unsigned long addr)
 {
        unsigned char *max_instr;
        unsigned char *instr;
-       int scan_more = 1;
        int prefetch = 0;
 
        /*
@@ -114,68 +160,22 @@ is_prefetch(struct pt_regs *regs, unsigned long error_code, unsigned long addr)
        if (error_code & PF_INSTR)
                return 0;
 
-       instr = (unsigned char *)convert_ip_to_linear(current, regs);
+       instr = (void *)convert_ip_to_linear(current, regs);
        max_instr = instr + 15;
 
        if (user_mode(regs) && instr >= (unsigned char *)TASK_SIZE)
                return 0;
 
-       while (scan_more && instr < max_instr) {
-               unsigned char instr_hi;
-               unsigned char instr_lo;
+       while (instr < max_instr) {
                unsigned char opcode;
 
                if (probe_kernel_address(instr, opcode))
                        break;
 
-               instr_hi = opcode & 0xf0;
-               instr_lo = opcode & 0x0f;
                instr++;
 
-               switch (instr_hi) {
-               case 0x20:
-               case 0x30:
-                       /*
-                        * Values 0x26,0x2E,0x36,0x3E are valid x86 prefixes.
-                        * In X86_64 long mode, the CPU will signal invalid
-                        * opcode if some of these prefixes are present so
-                        * X86_64 will never get here anyway
-                        */
-                       scan_more = ((instr_lo & 7) == 0x6);
-                       break;
-#ifdef CONFIG_X86_64
-               case 0x40:
-                       /*
-                        * In AMD64 long mode 0x40..0x4F are valid REX prefixes
-                        * Need to figure out under what instruction mode the
-                        * instruction was issued. Could check the LDT for lm,
-                        * but for now it's good enough to assume that long
-                        * mode only uses well known segments or kernel.
-                        */
-                       scan_more = (!user_mode(regs)) || (regs->cs == __USER_CS);
-                       break;
-#endif
-               case 0x60:
-                       /* 0x64 thru 0x67 are valid prefixes in all modes. */
-                       scan_more = (instr_lo & 0xC) == 0x4;
+               if (!check_prefetch_opcode(regs, instr, opcode, &prefetch))
                        break;
-               case 0xF0:
-                       /* 0xF0, 0xF2, 0xF3 are valid prefixes in all modes. */
-                       scan_more = !instr_lo || (instr_lo>>1) == 1;
-                       break;
-               case 0x00:
-                       /* Prefetch instruction is 0x0F0D or 0x0F18 */
-                       scan_more = 0;
-
-                       if (probe_kernel_address(instr, opcode))
-                               break;
-                       prefetch = (instr_lo == 0xF) &&
-                               (opcode == 0x0D || opcode == 0x18);
-                       break;
-               default:
-                       scan_more = 0;
-                       break;
-               }
        }
        return prefetch;
 }