Commit 107a0367 authored by Ingo Molnar's avatar Ingo Molnar
Browse files

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: default avatarIngo Molnar <mingo@elte.hu>
parent 2d4a7167

arch/x86/mm/fault.c

+50 −50
Original line number Diff line number Diff line
@@ -99,38 +99,12 @@ static inline int notify_page_fault(struct pt_regs *regs) 
 *

 * Opcode checker based on code by Richard Brunner.

 */

static int

is_prefetch(struct pt_regs *regs, unsigned long error_code, unsigned long addr)

static inline int

check_prefetch_opcode(struct pt_regs *regs, unsigned char *instr,

		      unsigned char opcode, int *prefetch)

{

	unsigned char *max_instr;

	unsigned char *instr;

	int scan_more = 1;

	int prefetch = 0;



	/*

	 * If it was a exec (instruction fetch) fault on NX page, then

	 * do not ignore the fault:

	 */

	if (error_code & PF_INSTR)

		return 0;



	instr = (unsigned char *)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;

		unsigned char opcode;



		if (probe_kernel_address(instr, opcode))

			break;



		instr_hi = opcode & 0xf0;

		instr_lo = opcode & 0x0f;

		instr++;

	unsigned char instr_hi = opcode & 0xf0;

	unsigned char instr_lo = opcode & 0x0f;



	switch (instr_hi) {

	case 0x20:
@@ -141,8 +115,7 @@ is_prefetch(struct pt_regs *regs, unsigned long error_code, unsigned long addr) 
		 * opcode if some of these prefixes are present so

		 * X86_64 will never get here anyway

		 */

			scan_more = ((instr_lo & 7) == 0x6);

			break;

		return ((instr_lo & 7) == 0x6);

#ifdef CONFIG_X86_64

	case 0x40:

		/*
@@ -152,30 +125,57 @@ is_prefetch(struct pt_regs *regs, unsigned long error_code, unsigned long addr) 
		 * 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;

		return (!user_mode(regs)) || (regs->cs == __USER_CS);

#endif

	case 0x60:

		/* 0x64 thru 0x67 are valid prefixes in all modes. */

			scan_more = (instr_lo & 0xC) == 0x4;

			break;

		return (instr_lo & 0xC) == 0x4;

	case 0xF0:

		/* 0xF0, 0xF2, 0xF3 are valid prefixes in all modes. */

			scan_more = !instr_lo || (instr_lo>>1) == 1;

			break;

		return !instr_lo || (instr_lo>>1) == 1;

	case 0x00:

		/* Prefetch instruction is 0x0F0D or 0x0F18 */

			scan_more = 0;



		if (probe_kernel_address(instr, opcode))

				break;

			prefetch = (instr_lo == 0xF) &&

			return 0;



		*prefetch = (instr_lo == 0xF) &&

			(opcode == 0x0D || opcode == 0x18);

			break;

		return 0;

	default:

			scan_more = 0;

			break;

		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 prefetch = 0;



	/*

	 * If it was a exec (instruction fetch) fault on NX page, then

	 * do not ignore the fault:

	 */

	if (error_code & PF_INSTR)

		return 0;



	instr = (void *)convert_ip_to_linear(current, regs);

	max_instr = instr + 15;



	if (user_mode(regs) && instr >= (unsigned char *)TASK_SIZE)

		return 0;



	while (instr < max_instr) {

		unsigned char opcode;



		if (probe_kernel_address(instr, opcode))

			break;



		instr++;



		if (!check_prefetch_opcode(regs, instr, opcode, &prefetch))

			break;

	}

	return prefetch;

}

CRA Git | Maintained and supported by SUSTech CRA and CCSE