ARM: ZERO_PAGE: Avoid flush_dcache_page() for zero page

[linux-2.6-block.git] / arch / arm / mm / flush.c

/*
 *  linux/arch/arm/mm/flush.c
 *
 *  Copyright (C) 1995-2002 Russell King
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */
#include <linux/module.h>
#include <linux/mm.h>
#include <linux/pagemap.h>

#include <asm/cacheflush.h>
#include <asm/cachetype.h>
#include <asm/system.h>
#include <asm/tlbflush.h>

#include "mm.h"

#ifdef CONFIG_CPU_CACHE_VIPT

#define ALIAS_FLUSH_START	0xffff4000

static void flush_pfn_alias(unsigned long pfn, unsigned long vaddr)
{
	unsigned long to = ALIAS_FLUSH_START + (CACHE_COLOUR(vaddr) << PAGE_SHIFT);
	const int zero = 0;

	set_pte_ext(TOP_PTE(to), pfn_pte(pfn, PAGE_KERNEL), 0);
	flush_tlb_kernel_page(to);

	asm(	"mcrr	p15, 0, %1, %0, c14\n"
	"	mcr	p15, 0, %2, c7, c10, 4"
	    :
	    : "r" (to), "r" (to + PAGE_SIZE - L1_CACHE_BYTES), "r" (zero)
	    : "cc");
	__flush_icache_all();
}

void flush_cache_mm(struct mm_struct *mm)
{
	if (cache_is_vivt()) {
		vivt_flush_cache_mm(mm);
		return;
	}

	if (cache_is_vipt_aliasing()) {
		asm(	"mcr	p15, 0, %0, c7, c14, 0\n"
		"	mcr	p15, 0, %0, c7, c10, 4"
		    :
		    : "r" (0)
		    : "cc");
		__flush_icache_all();
	}
}

void flush_cache_range(struct vm_area_struct *vma, unsigned long start, unsigned long end)
{
	if (cache_is_vivt()) {
		vivt_flush_cache_range(vma, start, end);
		return;
	}

	if (cache_is_vipt_aliasing()) {
		asm(	"mcr	p15, 0, %0, c7, c14, 0\n"
		"	mcr	p15, 0, %0, c7, c10, 4"
		    :
		    : "r" (0)
		    : "cc");
		__flush_icache_all();
	}
}

void flush_cache_page(struct vm_area_struct *vma, unsigned long user_addr, unsigned long pfn)
{
	if (cache_is_vivt()) {
		vivt_flush_cache_page(vma, user_addr, pfn);
		return;
	}

	if (cache_is_vipt_aliasing())
		flush_pfn_alias(pfn, user_addr);
}

void flush_ptrace_access(struct vm_area_struct *vma, struct page *page,
			 unsigned long uaddr, void *kaddr,
			 unsigned long len, int write)
{
	if (cache_is_vivt()) {
		vivt_flush_ptrace_access(vma, page, uaddr, kaddr, len, write);
		return;
	}

	if (cache_is_vipt_aliasing()) {
		flush_pfn_alias(page_to_pfn(page), uaddr);
		return;
	}

	/* VIPT non-aliasing cache */
	if (cpumask_test_cpu(smp_processor_id(), mm_cpumask(vma->vm_mm)) &&
	    vma->vm_flags & VM_EXEC) {
		unsigned long addr = (unsigned long)kaddr;
		/* only flushing the kernel mapping on non-aliasing VIPT */
		__cpuc_coherent_kern_range(addr, addr + len);
	}
}
#else
#define flush_pfn_alias(pfn,vaddr)	do { } while (0)
#endif

void __flush_dcache_page(struct address_space *mapping, struct page *page)
{
	void *addr = page_address(page);

	/*
	 * Writeback any data associated with the kernel mapping of this
	 * page.  This ensures that data in the physical page is mutually
	 * coherent with the kernels mapping.
	 */
#ifdef CONFIG_HIGHMEM
	/*
	 * kmap_atomic() doesn't set the page virtual address, and
	 * kunmap_atomic() takes care of cache flushing already.
	 */
	if (addr)
#endif
		__cpuc_flush_dcache_page(addr);

	/*
	 * If this is a page cache page, and we have an aliasing VIPT cache,
	 * we only need to do one flush - which would be at the relevant
	 * userspace colour, which is congruent with page->index.
	 */
	if (mapping && cache_is_vipt_aliasing())
		flush_pfn_alias(page_to_pfn(page),
				page->index << PAGE_CACHE_SHIFT);
}

static void __flush_dcache_aliases(struct address_space *mapping, struct page *page)
{
	struct mm_struct *mm = current->active_mm;
	struct vm_area_struct *mpnt;
	struct prio_tree_iter iter;
	pgoff_t pgoff;

	/*
	 * There are possible user space mappings of this page:
	 * - VIVT cache: we need to also write back and invalidate all user
	 *   data in the current VM view associated with this page.
	 * - aliasing VIPT: we only need to find one mapping of this page.
	 */
	pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);

	flush_dcache_mmap_lock(mapping);
	vma_prio_tree_foreach(mpnt, &iter, &mapping->i_mmap, pgoff, pgoff) {
		unsigned long offset;

		/*
		 * If this VMA is not in our MM, we can ignore it.
		 */
		if (mpnt->vm_mm != mm)
			continue;
		if (!(mpnt->vm_flags & VM_MAYSHARE))
			continue;
		offset = (pgoff - mpnt->vm_pgoff) << PAGE_SHIFT;
		flush_cache_page(mpnt, mpnt->vm_start + offset, page_to_pfn(page));
	}
	flush_dcache_mmap_unlock(mapping);
}

/*
 * Ensure cache coherency between kernel mapping and userspace mapping
 * of this page.
 *
 * We have three cases to consider:
 *  - VIPT non-aliasing cache: fully coherent so nothing required.
 *  - VIVT: fully aliasing, so we need to handle every alias in our
 *          current VM view.
 *  - VIPT aliasing: need to handle one alias in our current VM view.
 *
 * If we need to handle aliasing:
 *  If the page only exists in the page cache and there are no user
 *  space mappings, we can be lazy and remember that we may have dirty
 *  kernel cache lines for later.  Otherwise, we assume we have
 *  aliasing mappings.
 *
 * Note that we disable the lazy flush for SMP.
 */
void flush_dcache_page(struct page *page)
{
	struct address_space *mapping;

	/*
	 * The zero page is never written to, so never has any dirty
	 * cache lines, and therefore never needs to be flushed.
	 */
	if (page == ZERO_PAGE(0))
		return;

	mapping = page_mapping(page);

#ifndef CONFIG_SMP
	if (!PageHighMem(page) && mapping && !mapping_mapped(mapping))
		set_bit(PG_dcache_dirty, &page->flags);
	else
#endif
	{
		__flush_dcache_page(mapping, page);
		if (mapping && cache_is_vivt())
			__flush_dcache_aliases(mapping, page);
		else if (mapping)
			__flush_icache_all();
	}
}
EXPORT_SYMBOL(flush_dcache_page);

/*
 * Flush an anonymous page so that users of get_user_pages()
 * can safely access the data.  The expected sequence is:
 *
 *  get_user_pages()
 *    -> flush_anon_page
 *  memcpy() to/from page
 *  if written to page, flush_dcache_page()
 */
void __flush_anon_page(struct vm_area_struct *vma, struct page *page, unsigned long vmaddr)
{
	unsigned long pfn;

	/* VIPT non-aliasing caches need do nothing */
	if (cache_is_vipt_nonaliasing())
		return;

	/*
	 * Write back and invalidate userspace mapping.
	 */
	pfn = page_to_pfn(page);
	if (cache_is_vivt()) {
		flush_cache_page(vma, vmaddr, pfn);
	} else {
		/*
		 * For aliasing VIPT, we can flush an alias of the
		 * userspace address only.
		 */
		flush_pfn_alias(pfn, vmaddr);
	}

	/*
	 * Invalidate kernel mapping.  No data should be contained
	 * in this mapping of the page.  FIXME: this is overkill
	 * since we actually ask for a write-back and invalidate.
	 */
	__cpuc_flush_dcache_page(page_address(page));
}