mm: re-architect the VM_UNPAGED logic

This replaces the (in my opinion horrible) VM_UNMAPPED logic with very
explicit support for a "remapped page range" aka VM_PFNMAP.  It allows a
VM area to contain an arbitrary range of page table entries that the VM
never touches, and never considers to be normal pages.

Any user of "remap_pfn_range()" automatically gets this new
functionality, and doesn't even have to mark the pages reserved or
indeed mark them any other way.  It just works.  As a side effect, doing
mmap() on /dev/mem works for arbitrary ranges.

Sparc update from David in the next commit.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 7 insertions, 15 deletions

diff --git a/mm/fremap.c b/mm/fremap.c
index 007cbad9331e..f851775e09c2 100644
--- a/mm/fremap.c
+++ b/mm/fremap.c
@@ -27,24 +27,20 @@ static int zap_pte(struct mm_struct *mm, struct vm_area_struct *vma,
         struct page *page = NULL;
 
         if (pte_present(pte)) {
-                unsigned long pfn = pte_pfn(pte);
-                flush_cache_page(vma, addr, pfn);
+                flush_cache_page(vma, addr, pte_pfn(pte));
                 pte = ptep_clear_flush(vma, addr, ptep);
-                if (unlikely(!pfn_valid(pfn))) {
-                        print_bad_pte(vma, pte, addr);
-                        goto out;
+                page = vm_normal_page(vma, addr, pte);
+                if (page) {
+                        if (pte_dirty(pte))
+                                set_page_dirty(page);
+                        page_remove_rmap(page);
+                        page_cache_release(page);
                 }
-                page = pfn_to_page(pfn);
-                if (pte_dirty(pte))
-                        set_page_dirty(page);
-                page_remove_rmap(page);
-                page_cache_release(page);
         } else {
                 if (!pte_file(pte))
                         free_swap_and_cache(pte_to_swp_entry(pte));
                 pte_clear(mm, addr, ptep);
         }
-out:
         return !!page;
 }
 
@@ -65,8 +61,6 @@ int install_page(struct mm_struct *mm, struct vm_area_struct *vma,
         pte_t pte_val;
         spinlock_t *ptl;
 
-        BUG_ON(vma->vm_flags & VM_UNPAGED);
-
         pgd = pgd_offset(mm, addr);
         pud = pud_alloc(mm, pgd, addr);
         if (!pud)
@@ -122,8 +116,6 @@ int install_file_pte(struct mm_struct *mm, struct vm_area_struct *vma,
         pte_t pte_val;
         spinlock_t *ptl;
 
-        BUG_ON(vma->vm_flags & VM_UNPAGED);
-
         pgd = pgd_offset(mm, addr);
         pud = pud_alloc(mm, pgd, addr);
         if (!pud)