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![Nick Piggin](/assets/img/avatar_default.png)
Highmem code can leave ptes and tlb entries around for a given page even after kunmap, and after it has been freed. >From what I can gather, the PAT code may change the cache attributes of arbitrary physical addresses (ie. including highmem pages), which would result in aliases in the case that it operates on one of these lazy tlb highmem pages. Flushing kmaps should solve the problem. I've also just added code for conditional flushing if we haven't got any dangling highmem aliases -- this should help performance if we change page attributes frequently or systems that aren't using much highmem pages (eg. if < 4G RAM). Should be turned into 2 patches, but just for RFC... Signed-off-by: Ingo Molnar <mingo@elte.hu>
375 lines
8.7 KiB
C
375 lines
8.7 KiB
C
/*
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* High memory handling common code and variables.
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*
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* (C) 1999 Andrea Arcangeli, SuSE GmbH, andrea@suse.de
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* Gerhard Wichert, Siemens AG, Gerhard.Wichert@pdb.siemens.de
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*
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*
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* Redesigned the x86 32-bit VM architecture to deal with
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* 64-bit physical space. With current x86 CPUs this
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* means up to 64 Gigabytes physical RAM.
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*
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* Rewrote high memory support to move the page cache into
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* high memory. Implemented permanent (schedulable) kmaps
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* based on Linus' idea.
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*
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* Copyright (C) 1999 Ingo Molnar <mingo@redhat.com>
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*/
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#include <linux/mm.h>
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#include <linux/module.h>
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#include <linux/swap.h>
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#include <linux/bio.h>
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#include <linux/pagemap.h>
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#include <linux/mempool.h>
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#include <linux/blkdev.h>
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#include <linux/init.h>
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#include <linux/hash.h>
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#include <linux/highmem.h>
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#include <linux/blktrace_api.h>
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#include <asm/tlbflush.h>
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/*
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* Virtual_count is not a pure "count".
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* 0 means that it is not mapped, and has not been mapped
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* since a TLB flush - it is usable.
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* 1 means that there are no users, but it has been mapped
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* since the last TLB flush - so we can't use it.
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* n means that there are (n-1) current users of it.
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*/
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#ifdef CONFIG_HIGHMEM
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unsigned long totalhigh_pages __read_mostly;
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EXPORT_SYMBOL(totalhigh_pages);
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unsigned int nr_free_highpages (void)
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{
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pg_data_t *pgdat;
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unsigned int pages = 0;
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for_each_online_pgdat(pgdat) {
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pages += zone_page_state(&pgdat->node_zones[ZONE_HIGHMEM],
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NR_FREE_PAGES);
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if (zone_movable_is_highmem())
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pages += zone_page_state(
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&pgdat->node_zones[ZONE_MOVABLE],
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NR_FREE_PAGES);
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}
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return pages;
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}
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static int pkmap_count[LAST_PKMAP];
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static unsigned int last_pkmap_nr;
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static __cacheline_aligned_in_smp DEFINE_SPINLOCK(kmap_lock);
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pte_t * pkmap_page_table;
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static DECLARE_WAIT_QUEUE_HEAD(pkmap_map_wait);
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static void flush_all_zero_pkmaps(void)
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{
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int i;
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int need_flush = 0;
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flush_cache_kmaps();
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for (i = 0; i < LAST_PKMAP; i++) {
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struct page *page;
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/*
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* zero means we don't have anything to do,
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* >1 means that it is still in use. Only
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* a count of 1 means that it is free but
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* needs to be unmapped
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*/
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if (pkmap_count[i] != 1)
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continue;
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pkmap_count[i] = 0;
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/* sanity check */
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BUG_ON(pte_none(pkmap_page_table[i]));
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/*
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* Don't need an atomic fetch-and-clear op here;
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* no-one has the page mapped, and cannot get at
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* its virtual address (and hence PTE) without first
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* getting the kmap_lock (which is held here).
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* So no dangers, even with speculative execution.
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*/
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page = pte_page(pkmap_page_table[i]);
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pte_clear(&init_mm, (unsigned long)page_address(page),
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&pkmap_page_table[i]);
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set_page_address(page, NULL);
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need_flush = 1;
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}
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if (need_flush)
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flush_tlb_kernel_range(PKMAP_ADDR(0), PKMAP_ADDR(LAST_PKMAP));
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}
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/**
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* kmap_flush_unused - flush all unused kmap mappings in order to remove stray mappings
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*/
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void kmap_flush_unused(void)
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{
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spin_lock(&kmap_lock);
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flush_all_zero_pkmaps();
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spin_unlock(&kmap_lock);
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}
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static inline unsigned long map_new_virtual(struct page *page)
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{
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unsigned long vaddr;
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int count;
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start:
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count = LAST_PKMAP;
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/* Find an empty entry */
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for (;;) {
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last_pkmap_nr = (last_pkmap_nr + 1) & LAST_PKMAP_MASK;
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if (!last_pkmap_nr) {
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flush_all_zero_pkmaps();
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count = LAST_PKMAP;
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}
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if (!pkmap_count[last_pkmap_nr])
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break; /* Found a usable entry */
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if (--count)
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continue;
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/*
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* Sleep for somebody else to unmap their entries
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*/
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{
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DECLARE_WAITQUEUE(wait, current);
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__set_current_state(TASK_UNINTERRUPTIBLE);
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add_wait_queue(&pkmap_map_wait, &wait);
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spin_unlock(&kmap_lock);
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schedule();
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remove_wait_queue(&pkmap_map_wait, &wait);
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spin_lock(&kmap_lock);
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/* Somebody else might have mapped it while we slept */
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if (page_address(page))
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return (unsigned long)page_address(page);
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/* Re-start */
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goto start;
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}
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}
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vaddr = PKMAP_ADDR(last_pkmap_nr);
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set_pte_at(&init_mm, vaddr,
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&(pkmap_page_table[last_pkmap_nr]), mk_pte(page, kmap_prot));
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pkmap_count[last_pkmap_nr] = 1;
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set_page_address(page, (void *)vaddr);
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return vaddr;
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}
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/**
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* kmap_high - map a highmem page into memory
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* @page: &struct page to map
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*
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* Returns the page's virtual memory address.
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*
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* We cannot call this from interrupts, as it may block.
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*/
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void *kmap_high(struct page *page)
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{
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unsigned long vaddr;
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/*
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* For highmem pages, we can't trust "virtual" until
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* after we have the lock.
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*/
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spin_lock(&kmap_lock);
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vaddr = (unsigned long)page_address(page);
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if (!vaddr)
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vaddr = map_new_virtual(page);
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pkmap_count[PKMAP_NR(vaddr)]++;
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BUG_ON(pkmap_count[PKMAP_NR(vaddr)] < 2);
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spin_unlock(&kmap_lock);
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return (void*) vaddr;
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}
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EXPORT_SYMBOL(kmap_high);
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/**
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* kunmap_high - map a highmem page into memory
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* @page: &struct page to unmap
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*/
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void kunmap_high(struct page *page)
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{
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unsigned long vaddr;
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unsigned long nr;
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int need_wakeup;
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spin_lock(&kmap_lock);
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vaddr = (unsigned long)page_address(page);
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BUG_ON(!vaddr);
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nr = PKMAP_NR(vaddr);
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/*
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* A count must never go down to zero
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* without a TLB flush!
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*/
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need_wakeup = 0;
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switch (--pkmap_count[nr]) {
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case 0:
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BUG();
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case 1:
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/*
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* Avoid an unnecessary wake_up() function call.
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* The common case is pkmap_count[] == 1, but
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* no waiters.
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* The tasks queued in the wait-queue are guarded
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* by both the lock in the wait-queue-head and by
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* the kmap_lock. As the kmap_lock is held here,
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* no need for the wait-queue-head's lock. Simply
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* test if the queue is empty.
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*/
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need_wakeup = waitqueue_active(&pkmap_map_wait);
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}
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spin_unlock(&kmap_lock);
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/* do wake-up, if needed, race-free outside of the spin lock */
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if (need_wakeup)
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wake_up(&pkmap_map_wait);
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}
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EXPORT_SYMBOL(kunmap_high);
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#endif
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#if defined(HASHED_PAGE_VIRTUAL)
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#define PA_HASH_ORDER 7
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/*
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* Describes one page->virtual association
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*/
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struct page_address_map {
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struct page *page;
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void *virtual;
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struct list_head list;
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};
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/*
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* page_address_map freelist, allocated from page_address_maps.
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*/
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static struct list_head page_address_pool; /* freelist */
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static spinlock_t pool_lock; /* protects page_address_pool */
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/*
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* Hash table bucket
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*/
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static struct page_address_slot {
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struct list_head lh; /* List of page_address_maps */
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spinlock_t lock; /* Protect this bucket's list */
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} ____cacheline_aligned_in_smp page_address_htable[1<<PA_HASH_ORDER];
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static struct page_address_slot *page_slot(struct page *page)
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{
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return &page_address_htable[hash_ptr(page, PA_HASH_ORDER)];
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}
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/**
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* page_address - get the mapped virtual address of a page
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* @page: &struct page to get the virtual address of
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*
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* Returns the page's virtual address.
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*/
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void *page_address(struct page *page)
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{
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unsigned long flags;
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void *ret;
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struct page_address_slot *pas;
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if (!PageHighMem(page))
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return lowmem_page_address(page);
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pas = page_slot(page);
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ret = NULL;
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spin_lock_irqsave(&pas->lock, flags);
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if (!list_empty(&pas->lh)) {
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struct page_address_map *pam;
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list_for_each_entry(pam, &pas->lh, list) {
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if (pam->page == page) {
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ret = pam->virtual;
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goto done;
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}
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}
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}
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done:
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spin_unlock_irqrestore(&pas->lock, flags);
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return ret;
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}
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EXPORT_SYMBOL(page_address);
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/**
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* set_page_address - set a page's virtual address
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* @page: &struct page to set
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* @virtual: virtual address to use
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*/
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void set_page_address(struct page *page, void *virtual)
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{
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unsigned long flags;
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struct page_address_slot *pas;
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struct page_address_map *pam;
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BUG_ON(!PageHighMem(page));
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pas = page_slot(page);
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if (virtual) { /* Add */
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BUG_ON(list_empty(&page_address_pool));
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spin_lock_irqsave(&pool_lock, flags);
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pam = list_entry(page_address_pool.next,
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struct page_address_map, list);
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list_del(&pam->list);
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spin_unlock_irqrestore(&pool_lock, flags);
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pam->page = page;
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pam->virtual = virtual;
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spin_lock_irqsave(&pas->lock, flags);
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list_add_tail(&pam->list, &pas->lh);
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spin_unlock_irqrestore(&pas->lock, flags);
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} else { /* Remove */
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spin_lock_irqsave(&pas->lock, flags);
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list_for_each_entry(pam, &pas->lh, list) {
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if (pam->page == page) {
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list_del(&pam->list);
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spin_unlock_irqrestore(&pas->lock, flags);
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spin_lock_irqsave(&pool_lock, flags);
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list_add_tail(&pam->list, &page_address_pool);
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spin_unlock_irqrestore(&pool_lock, flags);
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goto done;
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}
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}
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spin_unlock_irqrestore(&pas->lock, flags);
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}
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done:
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return;
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}
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static struct page_address_map page_address_maps[LAST_PKMAP];
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void __init page_address_init(void)
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{
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int i;
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INIT_LIST_HEAD(&page_address_pool);
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for (i = 0; i < ARRAY_SIZE(page_address_maps); i++)
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list_add(&page_address_maps[i].list, &page_address_pool);
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for (i = 0; i < ARRAY_SIZE(page_address_htable); i++) {
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INIT_LIST_HEAD(&page_address_htable[i].lh);
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spin_lock_init(&page_address_htable[i].lock);
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}
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spin_lock_init(&pool_lock);
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}
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#endif /* defined(CONFIG_HIGHMEM) && !defined(WANT_PAGE_VIRTUAL) */
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