1 files changed, 260 insertions, 0 deletions
diff --git a/mm/fremap.c b/mm/fremap.c
new file mode 100644
index 0000000..b602c27
--- /dev/null
+++ b/mm/fremap.c
@@ -0,0 +1,260 @@
+/*
+ *   linux/mm/fremap.c
+ * 
+ * Explicit pagetable population and nonlinear (random) mappings support.
+ *
+ * started by Ingo Molnar, Copyright (C) 2002, 2003
+ */
+#include <linux/backing-dev.h>
+#include <linux/mm.h>
+#include <linux/swap.h>
+#include <linux/file.h>
+#include <linux/mman.h>
+#include <linux/pagemap.h>
+#include <linux/swapops.h>
+#include <linux/rmap.h>
+#include <linux/module.h>
+#include <linux/syscalls.h>
+#include <linux/mmu_notifier.h>
+
+#include <asm/mmu_context.h>
+#include <asm/cacheflush.h>
+#include <asm/tlbflush.h>
+
+#include "internal.h"
+
+static void zap_pte(struct mm_struct *mm, struct vm_area_struct *vma,
+			unsigned long addr, pte_t *ptep)
+{
+	pte_t pte = *ptep;
+
+	if (pte_present(pte)) {
+		struct page *page;
+
+		flush_cache_page(vma, addr, pte_pfn(pte));
+		pte = ptep_clear_flush(vma, addr, ptep);
+		page = vm_normal_page(vma, addr, pte);
+		if (page) {
+			if (pte_dirty(pte))
+				set_page_dirty(page);
+			page_remove_rmap(page, vma);
+			page_cache_release(page);
+			update_hiwater_rss(mm);
+			dec_mm_counter(mm, file_rss);
+		}
+	} else {
+		if (!pte_file(pte))
+			free_swap_and_cache(pte_to_swp_entry(pte));
+		pte_clear_not_present_full(mm, addr, ptep, 0);
+	}
+}
+
+/*
+ * Install a file pte to a given virtual memory address, release any
+ * previously existing mapping.
+ */
+static int install_file_pte(struct mm_struct *mm, struct vm_area_struct *vma,
+		unsigned long addr, unsigned long pgoff, pgprot_t prot)
+{
+	int err = -ENOMEM;
+	pte_t *pte;
+	spinlock_t *ptl;
+
+	pte = get_locked_pte(mm, addr, &ptl);
+	if (!pte)
+		goto out;
+
+	if (!pte_none(*pte))
+		zap_pte(mm, vma, addr, pte);
+
+	set_pte_at(mm, addr, pte, pgoff_to_pte(pgoff));
+	/*
+	 * We don't need to run update_mmu_cache() here because the "file pte"
+	 * being installed by install_file_pte() is not a real pte - it's a
+	 * non-present entry (like a swap entry), noting what file offset should
+	 * be mapped there when there's a fault (in a non-linear vma where
+	 * that's not obvious).
+	 */
+	pte_unmap_unlock(pte, ptl);
+	err = 0;
+out:
+	return err;
+}
+
+static int populate_range(struct mm_struct *mm, struct vm_area_struct *vma,
+			unsigned long addr, unsigned long size, pgoff_t pgoff)
+{
+	int err;
+
+	do {
+		err = install_file_pte(mm, vma, addr, pgoff, vma->vm_page_prot);
+		if (err)
+			return err;
+
+		size -= PAGE_SIZE;
+		addr += PAGE_SIZE;
+		pgoff++;
+	} while (size);
+
+        return 0;
+
+}
+
+/**
+ * sys_remap_file_pages - remap arbitrary pages of an existing VM_SHARED vma
+ * @start: start of the remapped virtual memory range
+ * @size: size of the remapped virtual memory range
+ * @prot: new protection bits of the range (see NOTE)
+ * @pgoff: to-be-mapped page of the backing store file
+ * @flags: 0 or MAP_NONBLOCKED - the later will cause no IO.
+ *
+ * sys_remap_file_pages remaps arbitrary pages of an existing VM_SHARED vma
+ * (shared backing store file).
+ *
+ * This syscall works purely via pagetables, so it's the most efficient
+ * way to map the same (large) file into a given virtual window. Unlike
+ * mmap()/mremap() it does not create any new vmas. The new mappings are
+ * also safe across swapout.
+ *
+ * NOTE: the @prot parameter right now is ignored (but must be zero),
+ * and the vma's default protection is used. Arbitrary protections
+ * might be implemented in the future.
+ */
+SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
+		unsigned long, prot, unsigned long, pgoff, unsigned long, flags)
+{
+	struct mm_struct *mm = current->mm;
+	struct address_space *mapping;
+	unsigned long end = start + size;
+	struct vm_area_struct *vma;
+	int err = -EINVAL;
+	int has_write_lock = 0;
+
+	if (prot)
+		return err;
+	/*
+	 * Sanitize the syscall parameters:
+	 */
+	start = start & PAGE_MASK;
+	size = size & PAGE_MASK;
+
+	/* Does the address range wrap, or is the span zero-sized? */
+	if (start + size <= start)
+		return err;
+
+	/* Can we represent this offset inside this architecture's pte's? */
+#if PTE_FILE_MAX_BITS < BITS_PER_LONG
+	if (pgoff + (size >> PAGE_SHIFT) >= (1UL << PTE_FILE_MAX_BITS))
+		return err;
+#endif
+
+	/* We need down_write() to change vma->vm_flags. */
+	down_read(&mm->mmap_sem);
+ retry:
+	vma = find_vma(mm, start);
+
+	/*
+	 * Make sure the vma is shared, that it supports prefaulting,
+	 * and that the remapped range is valid and fully within
+	 * the single existing vma.  vm_private_data is used as a
+	 * swapout cursor in a VM_NONLINEAR vma.
+	 */
+	if (!vma || !(vma->vm_flags & VM_SHARED))
+		goto out;
+
+	if (vma->vm_private_data && !(vma->vm_flags & VM_NONLINEAR))
+		goto out;
+
+	if (!(vma->vm_flags & VM_CAN_NONLINEAR))
+		goto out;
+
+	if (end <= start || start < vma->vm_start || end > vma->vm_end)
+		goto out;
+
+	/* Must set VM_NONLINEAR before any pages are populated. */
+	if (!(vma->vm_flags & VM_NONLINEAR)) {
+		/* Don't need a nonlinear mapping, exit success */
+		if (pgoff == linear_page_index(vma, start)) {
+			err = 0;
+			goto out;
+		}
+
+		if (!has_write_lock) {
+			up_read(&mm->mmap_sem);
+			down_write(&mm->mmap_sem);
+			has_write_lock = 1;
+			goto retry;
+		}
+		mapping = vma->vm_file->f_mapping;
+		/*
+		 * page_mkclean doesn't work on nonlinear vmas, so if
+		 * dirty pages need to be accounted, emulate with linear
+		 * vmas.
+		 */
+		if (mapping_cap_account_dirty(mapping)) {
+			unsigned long addr;
+			struct file *file = vma->vm_file;
+
+			flags &= MAP_NONBLOCK;
+			get_file(file);
+			addr = mmap_region(file, start, size,
+					flags, vma->vm_flags, pgoff, 1);
+			fput(file);
+			if (IS_ERR_VALUE(addr)) {
+				err = addr;
+			} else {
+				BUG_ON(addr != start);
+				err = 0;
+			}
+			goto out;
+		}
+		spin_lock(&mapping->i_mmap_lock);
+		flush_dcache_mmap_lock(mapping);
+		vma->vm_flags |= VM_NONLINEAR;
+		vma_prio_tree_remove(vma, &mapping->i_mmap);
+		vma_nonlinear_insert(vma, &mapping->i_mmap_nonlinear);
+		flush_dcache_mmap_unlock(mapping);
+		spin_unlock(&mapping->i_mmap_lock);
+	}
+
+	if (vma->vm_flags & VM_LOCKED) {
+		/*
+		 * drop PG_Mlocked flag for over-mapped range
+		 */
+		unsigned int saved_flags = vma->vm_flags;
+		munlock_vma_pages_range(vma, start, start + size);
+		vma->vm_flags = saved_flags;
+	}
+
+	mmu_notifier_invalidate_range_start(mm, start, start + size);
+	err = populate_range(mm, vma, start, size, pgoff);
+	mmu_notifier_invalidate_range_end(mm, start, start + size);
+	if (!err && !(flags & MAP_NONBLOCK)) {
+		if (vma->vm_flags & VM_LOCKED) {
+			/*
+			 * might be mapping previously unmapped range of file
+			 */
+			mlock_vma_pages_range(vma, start, start + size);
+		} else {
+			if (unlikely(has_write_lock)) {
+				downgrade_write(&mm->mmap_sem);
+				has_write_lock = 0;
+			}
+			make_pages_present(start, start+size);
+		}
+	}
+
+	/*
+	 * We can't clear VM_NONLINEAR because we'd have to do
+	 * it after ->populate completes, and that would prevent
+	 * downgrading the lock.  (Locks can't be upgraded).
+	 */
+
+out:
+	if (likely(!has_write_lock))
+		up_read(&mm->mmap_sem);
+	else
+		up_write(&mm->mmap_sem);
+
+	return err;
+}