text: // SPDX-License-Identifier: GPL-2.0
  /*
   * highmem.c: virtual kernel memory mappings for high memory
   *
   * PowerPC version, stolen from the i386 version.
   *
   * Used in CONFIG_HIGHMEM systems for memory pages which
   * are not addressable by direct kernel virtual addresses.
   *
   * Copyright (C) 1999 Gerhard Wichert, Siemens AG
   *		      Gerhard.Wichert@pdb.siemens.de
   *
   *
   * Redesigned the x86 32-bit VM architecture to deal with
   * up to 16 Terrabyte physical memory. With current x86 CPUs
   * we now support up to 64 Gigabytes physical RAM.
   *
   * Copyright (C) 1999 Ingo Molnar <mingo@redhat.com>
   *
   * Reworked for PowerPC by various contributors. Moved from
   * highmem.h by Benjamin Herrenschmidt (c) 2009 IBM Corp.
   */
  
  #include <linux/highmem.h>
  #include <linux/module.h>
  
  /*
   * The use of kmap_atomic/kunmap_atomic is discouraged - kmap/kunmap
   * gives a more generic (and caching) interface. But kmap_atomic can
   * be used in IRQ contexts, so in some (very limited) cases we need
   * it.
   */
  void *kmap_atomic_prot(struct page *page, pgprot_t prot)
  {
  	unsigned long vaddr;
  	int idx, type;
  
  	preempt_disable();
  	pagefault_disable();
  	if (!PageHighMem(page))
  		return page_address(page);
  
  	type = kmap_atomic_idx_push();
  	idx = type + KM_TYPE_NR*smp_processor_id();
  	vaddr = __fix_to_virt(FIX_KMAP_BEGIN + idx);
  #ifdef CONFIG_DEBUG_HIGHMEM
  	BUG_ON(!pte_none(*(kmap_pte-idx)));
  #endif
  	__set_pte_at(&init_mm, vaddr, kmap_pte-idx, mk_pte(page, prot), 1);
  	local_flush_tlb_page(NULL, vaddr);
  
  	return (void*) vaddr;
  }
  EXPORT_SYMBOL(kmap_atomic_prot);
  
  void __kunmap_atomic(void *kvaddr)
  {
  	unsigned long vaddr = (unsigned long) kvaddr & PAGE_MASK;
  	int type;
  
  	if (vaddr < __fix_to_virt(FIX_KMAP_END)) {
  		pagefault_enable();
  		preempt_enable();
  		return;
  	}
  
  	type = kmap_atomic_idx();
  
  #ifdef CONFIG_DEBUG_HIGHMEM
  	{
  		unsigned int idx;
  
  		idx = type + KM_TYPE_NR * smp_processor_id();
  		BUG_ON(vaddr != __fix_to_virt(FIX_KMAP_BEGIN + idx));
  
  		/*
  		 * force other mappings to Oops if they'll try to access
  		 * this pte without first remap it
  		 */
  		pte_clear(&init_mm, vaddr, kmap_pte-idx);
  		local_flush_tlb_page(NULL, vaddr);
  	}
  #endif
  
  	kmap_atomic_idx_pop();
  	pagefault_enable();
  	preempt_enable();
  }
  EXPORT_SYMBOL(__kunmap_atomic);
  