/* include/asm-generic/tlb.h
   *
   *	Generic TLB shootdown code
   *
   * Copyright 2001 Red Hat, Inc.
   * Based on code from mm/memory.c Copyright Linus Torvalds and others.
   *
   * Copyright 2011 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public License
   * as published by the Free Software Foundation; either version
   * 2 of the License, or (at your option) any later version.
   */
  #ifndef _ASM_GENERIC__TLB_H
  #define _ASM_GENERIC__TLB_H
  
  #include <linux/swap.h>
  #include <asm/pgalloc.h>
  #include <asm/tlbflush.h>
  
  #ifdef CONFIG_HAVE_RCU_TABLE_FREE
  /*
   * Semi RCU freeing of the page directories.
   *
   * This is needed by some architectures to implement software pagetable walkers.
   *
   * gup_fast() and other software pagetable walkers do a lockless page-table
   * walk and therefore needs some synchronization with the freeing of the page
   * directories. The chosen means to accomplish that is by disabling IRQs over
   * the walk.
   *
   * Architectures that use IPIs to flush TLBs will then automagically DTRT,
   * since we unlink the page, flush TLBs, free the page. Since the disabling of
   * IRQs delays the completion of the TLB flush we can never observe an already
   * freed page.
   *
   * Architectures that do not have this (PPC) need to delay the freeing by some
   * other means, this is that means.
   *
   * What we do is batch the freed directory pages (tables) and RCU free them.
   * We use the sched RCU variant, as that guarantees that IRQ/preempt disabling
   * holds off grace periods.
   *
   * However, in order to batch these pages we need to allocate storage, this
   * allocation is deep inside the MM code and can thus easily fail on memory
   * pressure. To guarantee progress we fall back to single table freeing, see
   * the implementation of tlb_remove_table_one().
   *
   */
  struct mmu_table_batch {
  	struct rcu_head		rcu;
  	unsigned int		nr;
  	void			*tables[0];
  };
  
  #define MAX_TABLE_BATCH		\
  	((PAGE_SIZE - sizeof(struct mmu_table_batch)) / sizeof(void *))
  
  extern void tlb_table_flush(struct mmu_gather *tlb);
  extern void tlb_remove_table(struct mmu_gather *tlb, void *table);
  
  #endif
  
  /*
   * If we can't allocate a page to make a big batch of page pointers
   * to work on, then just handle a few from the on-stack structure.
   */
  #define MMU_GATHER_BUNDLE	8
  
  struct mmu_gather_batch {
  	struct mmu_gather_batch	*next;
  	unsigned int		nr;
  	unsigned int		max;
  	struct page		*pages[0];
  };
  
  #define MAX_GATHER_BATCH	\
  	((PAGE_SIZE - sizeof(struct mmu_gather_batch)) / sizeof(void *))
  
  /*
   * Limit the maximum number of mmu_gather batches to reduce a risk of soft
   * lockups for non-preemptible kernels on huge machines when a lot of memory
   * is zapped during unmapping.
   * 10K pages freed at once should be safe even without a preemption point.
   */
  #define MAX_GATHER_BATCH_COUNT	(10000UL/MAX_GATHER_BATCH)
  
  /* struct mmu_gather is an opaque type used by the mm code for passing around
   * any data needed by arch specific code for tlb_remove_page.
   */
  struct mmu_gather {
  	struct mm_struct	*mm;
  #ifdef CONFIG_HAVE_RCU_TABLE_FREE
  	struct mmu_table_batch	*batch;
  #endif
  	unsigned long		start;
  	unsigned long		end;
  	unsigned int		need_flush : 1,	/* Did free PTEs */
  	/* we are in the middle of an operation to clear
  	 * a full mm and can make some optimizations */
  				fullmm : 1,
  	/* we have performed an operation which
  	 * requires a complete flush of the tlb */
  				need_flush_all : 1;
  
  	struct mmu_gather_batch *active;
  	struct mmu_gather_batch	local;
  	struct page		*__pages[MMU_GATHER_BUNDLE];
  	unsigned int		batch_count;
  };
  
  #define HAVE_GENERIC_MMU_GATHER
  
  void tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm, unsigned long start, unsigned long end);
  void tlb_flush_mmu(struct mmu_gather *tlb);
  void tlb_finish_mmu(struct mmu_gather *tlb, unsigned long start,
  							unsigned long end);
  int __tlb_remove_page(struct mmu_gather *tlb, struct page *page);
  
  /* tlb_remove_page
   *	Similar to __tlb_remove_page but will call tlb_flush_mmu() itself when
   *	required.
   */
  static inline void tlb_remove_page(struct mmu_gather *tlb, struct page *page)
  {
  	if (!__tlb_remove_page(tlb, page))
  		tlb_flush_mmu(tlb);
  }
  
  /**
   * tlb_remove_tlb_entry - remember a pte unmapping for later tlb invalidation.
   *
   * Record the fact that pte's were really umapped in ->need_flush, so we can
   * later optimise away the tlb invalidate.   This helps when userspace is
   * unmapping already-unmapped pages, which happens quite a lot.
   */
  #define tlb_remove_tlb_entry(tlb, ptep, address)		\
  	do {							\
  		tlb->need_flush = 1;				\
  		__tlb_remove_tlb_entry(tlb, ptep, address);	\
  	} while (0)
  
  /**
   * tlb_remove_pmd_tlb_entry - remember a pmd mapping for later tlb invalidation
   * This is a nop so far, because only x86 needs it.
   */
  #ifndef __tlb_remove_pmd_tlb_entry
  #define __tlb_remove_pmd_tlb_entry(tlb, pmdp, address) do {} while (0)
  #endif
  
  #define tlb_remove_pmd_tlb_entry(tlb, pmdp, address)		\
  	do {							\
  		tlb->need_flush = 1;				\
  		__tlb_remove_pmd_tlb_entry(tlb, pmdp, address);	\
  	} while (0)
  
  #define pte_free_tlb(tlb, ptep, address)			\
  	do {							\
  		tlb->need_flush = 1;				\
  		__pte_free_tlb(tlb, ptep, address);		\
  	} while (0)
  
  #ifndef __ARCH_HAS_4LEVEL_HACK
  #define pud_free_tlb(tlb, pudp, address)			\
  	do {							\
  		tlb->need_flush = 1;				\
  		__pud_free_tlb(tlb, pudp, address);		\
  	} while (0)
  #endif
  
  #define pmd_free_tlb(tlb, pmdp, address)			\
  	do {							\
  		tlb->need_flush = 1;				\
  		__pmd_free_tlb(tlb, pmdp, address);		\
  	} while (0)
  
  #define tlb_migrate_finish(mm) do {} while (0)
  
  #endif /* _ASM_GENERIC__TLB_H */