text: /*
   * Access kernel memory without faulting -- s390 specific implementation.
   *
   * Copyright IBM Corp. 2009
   *
   *   Author(s): Heiko Carstens <heiko.carstens@de.ibm.com>,
   *
   */
  
  #include <linux/uaccess.h>
  #include <linux/kernel.h>
  #include <linux/types.h>
  #include <linux/errno.h>
  #include <linux/gfp.h>
  #include <linux/cpu.h>
  #include <asm/ctl_reg.h>
  #include <asm/io.h>
  
  /*
   * This function writes to kernel memory bypassing DAT and possible
   * write protection. It copies one to four bytes from src to dst
   * using the stura instruction.
   * Returns the number of bytes copied or -EFAULT.
   */
  static long probe_kernel_write_odd(void *dst, const void *src, size_t size)
  {
  	unsigned long count, aligned;
  	int offset, mask;
  	int rc = -EFAULT;
  
  	aligned = (unsigned long) dst & ~3UL;
  	offset = (unsigned long) dst & 3;
  	count = min_t(unsigned long, 4 - offset, size);
  	mask = (0xf << (4 - count)) & 0xf;
  	mask >>= offset;
  	asm volatile(
  		"	bras	1,0f\n"
  		"	icm	0,0,0(%3)\n"
  		"0:	l	0,0(%1)\n"
  		"	lra	%1,0(%1)\n"
  		"1:	ex	%2,0(1)\n"
  		"2:	stura	0,%1\n"
  		"	la	%0,0\n"
  		"3:\n"
  		EX_TABLE(0b,3b) EX_TABLE(1b,3b) EX_TABLE(2b,3b)
  		: "+d" (rc), "+a" (aligned)
  		: "a" (mask), "a" (src) : "cc", "memory", "0", "1");
  	return rc ? rc : count;
  }
  
  long probe_kernel_write(void *dst, const void *src, size_t size)
  {
  	long copied = 0;
  
  	while (size) {
  		copied = probe_kernel_write_odd(dst, src, size);
  		if (copied < 0)
  			break;
  		dst += copied;
  		src += copied;
  		size -= copied;
  	}
  	return copied < 0 ? -EFAULT : 0;
  }
  
  static int __memcpy_real(void *dest, void *src, size_t count)
  {
  	register unsigned long _dest asm("2") = (unsigned long) dest;
  	register unsigned long _len1 asm("3") = (unsigned long) count;
  	register unsigned long _src  asm("4") = (unsigned long) src;
  	register unsigned long _len2 asm("5") = (unsigned long) count;
  	int rc = -EFAULT;
  
  	asm volatile (
  		"0:	mvcle	%1,%2,0x0\n"
  		"1:	jo	0b\n"
  		"	lhi	%0,0x0\n"
  		"2:\n"
  		EX_TABLE(1b,2b)
  		: "+d" (rc), "+d" (_dest), "+d" (_src), "+d" (_len1),
  		  "+d" (_len2), "=m" (*((long *) dest))
  		: "m" (*((long *) src))
  		: "cc", "memory");
  	return rc;
  }
  
  /*
   * Copy memory in real mode (kernel to kernel)
   */
  int memcpy_real(void *dest, void *src, size_t count)
  {
  	unsigned long flags;
  	int rc;
  
  	if (!count)
  		return 0;
  	local_irq_save(flags);
  	__arch_local_irq_stnsm(0xfbUL);
  	rc = __memcpy_real(dest, src, count);
  	local_irq_restore(flags);
  	return rc;
  }
  
  /*
   * Copy memory in absolute mode (kernel to kernel)
   */
  void memcpy_absolute(void *dest, void *src, size_t count)
  {
  	unsigned long cr0, flags, prefix;
  
  	flags = arch_local_irq_save();
  	__ctl_store(cr0, 0, 0);
  	__ctl_clear_bit(0, 28); /* disable lowcore protection */
  	prefix = store_prefix();
  	if (prefix) {
  		local_mcck_disable();
  		set_prefix(0);
  		memcpy(dest, src, count);
  		set_prefix(prefix);
  		local_mcck_enable();
  	} else {
  		memcpy(dest, src, count);
  	}
  	__ctl_load(cr0, 0, 0);
  	arch_local_irq_restore(flags);
  }
  
  /*
   * Copy memory from kernel (real) to user (virtual)
   */
  int copy_to_user_real(void __user *dest, void *src, size_t count)
  {
  	int offs = 0, size, rc;
  	char *buf;
  
  	buf = (char *) __get_free_page(GFP_KERNEL);
  	if (!buf)
  		return -ENOMEM;
  	rc = -EFAULT;
  	while (offs < count) {
  		size = min(PAGE_SIZE, count - offs);
  		if (memcpy_real(buf, src + offs, size))
  			goto out;
  		if (copy_to_user(dest + offs, buf, size))
  			goto out;
  		offs += size;
  	}
  	rc = 0;
  out:
  	free_page((unsigned long) buf);
  	return rc;
  }
  
  /*
   * Copy memory from user (virtual) to kernel (real)
   */
  int copy_from_user_real(void *dest, void __user *src, size_t count)
  {
  	int offs = 0, size, rc;
  	char *buf;
  
  	buf = (char *) __get_free_page(GFP_KERNEL);
  	if (!buf)
  		return -ENOMEM;
  	rc = -EFAULT;
  	while (offs < count) {
  		size = min(PAGE_SIZE, count - offs);
  		if (copy_from_user(buf, src + offs, size))
  			goto out;
  		if (memcpy_real(dest + offs, buf, size))
  			goto out;
  		offs += size;
  	}
  	rc = 0;
  out:
  	free_page((unsigned long) buf);
  	return rc;
  }
  
  /*
   * Check if physical address is within prefix or zero page
   */
  static int is_swapped(unsigned long addr)
  {
  	unsigned long lc;
  	int cpu;
  
  	if (addr < sizeof(struct _lowcore))
  		return 1;
  	for_each_online_cpu(cpu) {
  		lc = (unsigned long) lowcore_ptr[cpu];
  		if (addr > lc + sizeof(struct _lowcore) - 1 || addr < lc)
  			continue;
  		return 1;
  	}
  	return 0;
  }
  
  /*
   * Convert a physical pointer for /dev/mem access
   *
   * For swapped prefix pages a new buffer is returned that contains a copy of
   * the absolute memory. The buffer size is maximum one page large.
   */
  void *xlate_dev_mem_ptr(unsigned long addr)
  {
  	void *bounce = (void *) addr;
  	unsigned long size;
  
  	get_online_cpus();
  	preempt_disable();
  	if (is_swapped(addr)) {
  		size = PAGE_SIZE - (addr & ~PAGE_MASK);
  		bounce = (void *) __get_free_page(GFP_ATOMIC);
  		if (bounce)
  			memcpy_absolute(bounce, (void *) addr, size);
  	}
  	preempt_enable();
  	put_online_cpus();
  	return bounce;
  }
  
  /*
   * Free converted buffer for /dev/mem access (if necessary)
   */
  void unxlate_dev_mem_ptr(unsigned long addr, void *buf)
  {
  	if ((void *) addr != buf)
  		free_page((unsigned long) buf);
  }
  