Support strange discontiguous PFN remappings

These get created by some drivers that don't generally even want a pfn
remapping at all, but would really mostly prefer to just map pages
they've allocated individually instead.

For now, create a helper function that turns such an incomplete PFN
remapping call into a loop that does that explicit mapping.  In the long
run we almost certainly want to export a totally different interface for
that, though.

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

2 files changed, 93 insertions, 0 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 6a75a7a78bf1..74f90d7eb5ef 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -163,6 +163,7 @@ extern unsigned int kobjsize(const void *objp);
 #define VM_HUGETLB      0x00400000      /* Huge TLB Page VM */
 #define VM_NONLINEAR    0x00800000      /* Is non-linear (remap_file_pages) */
 #define VM_MAPPED_COPY  0x01000000      /* T if mapped copy of data (nommu mmap) */
+#define VM_INCOMPLETE   0x02000000      /* Strange partial PFN mapping marker */
 
 #ifndef VM_STACK_DEFAULT_FLAGS          /* arch can override this */
 #define VM_STACK_DEFAULT_FLAGS VM_DATA_DEFAULT_FLAGS
diff --git a/mm/memory.c b/mm/memory.c
index 74839b3a3999..990e7dc666f8 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1147,6 +1147,95 @@ int zeromap_page_range(struct vm_area_struct *vma,
 }
 
 /*
+ * This is the old fallback for page remapping.
+ *
+ * For historical reasons, it only allows reserved pages. Only
+ * old drivers should use this, and they needed to mark their
+ * pages reserved for the old functions anyway.
+ */
+static int insert_page(struct mm_struct *mm, unsigned long addr, struct page *page, pgprot_t prot)
+{
+        int retval;
+        pgd_t * pgd;
+        pud_t * pud;
+        pmd_t * pmd;  
+        pte_t * pte;
+        spinlock_t *ptl;  
+
+        retval = -EINVAL;
+        if (PageAnon(page) || !PageReserved(page))
+                goto out;
+        retval = -ENOMEM;
+        flush_dcache_page(page);
+        pgd = pgd_offset(mm, addr);
+        pud = pud_alloc(mm, pgd, addr);
+        if (!pud)
+                goto out;
+        pmd = pmd_alloc(mm, pud, addr);
+        if (!pmd)
+                goto out;
+        pte = pte_alloc_map_lock(mm, pmd, addr, &ptl);
+        if (!pte)
+                goto out;
+        retval = -EBUSY;
+        if (!pte_none(*pte))
+                goto out_unlock;
+
+        /* Ok, finally just insert the thing.. */
+        get_page(page);
+        inc_mm_counter(mm, file_rss);
+        page_add_file_rmap(page);
+        set_pte_at(mm, addr, pte, mk_pte(page, prot));
+
+        retval = 0;
+out_unlock:
+        pte_unmap_unlock(pte, ptl);
+out:
+        return retval;
+}
+
+/*
+ * Somebody does a pfn remapping that doesn't actually work as a vma.
+ *
+ * Do it as individual pages instead, and warn about it. It's bad form,
+ * and very inefficient.
+ */
+static int incomplete_pfn_remap(struct vm_area_struct *vma,
+                unsigned long start, unsigned long end,
+                unsigned long pfn, pgprot_t prot)
+{
+        static int warn = 10;
+        struct page *page;
+        int retval;
+
+        if (!(vma->vm_flags & VM_INCOMPLETE)) {
+                if (warn) {
+                        warn--;
+                        printk("%s does an incomplete pfn remapping", current->comm);
+                        dump_stack();
+                }
+        }
+        vma->vm_flags |= VM_INCOMPLETE | VM_IO | VM_RESERVED;
+
+        if (start < vma->vm_start || end > vma->vm_end)
+                return -EINVAL;
+
+        if (!pfn_valid(pfn))
+                return -EINVAL;
+
+        retval = 0;
+        page = pfn_to_page(pfn);
+        while (start < end) {
+                retval = insert_page(vma->vm_mm, start, page, prot);
+                if (retval < 0)
+                        break;
+                start += PAGE_SIZE;
+                page++;
+        }
+        return retval;
+}
+
+/*
  * maps a range of physical memory into the requested pages. the old
  * mappings are removed. any references to nonexistent pages results
  * in null mappings (currently treated as "copy-on-access")
@@ -1220,6 +1309,9 @@ int remap_pfn_range(struct vm_area_struct *vma, unsigned long addr,
         struct mm_struct *mm = vma->vm_mm;
         int err;
 
+        if (addr != vma->vm_start || end != vma->vm_end)
+                return incomplete_pfn_remap(vma, addr, end, pfn, prot);
+
         /*
          * Physically remapped pages are special. Tell the
          * rest of the world about it: