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>

1 files changed, 50 insertions, 50 deletions

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 351d679bf977..72973c7682ba 100644
--- 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;
 }