[PATCH v2 16/16] kcov: update kcov to use mmap_prepare

[Lorenzo Stoakes]

We can use the mmap insert pages functionality provided for use in
mmap_prepare to insert the kcov pages as required.

This does necessitate an allocation, but since it's in the mmap path this
doesn't seem egregious. The allocation/freeing of the pages array is
handled automatically by vma_desc_set_mixedmap_pages() and the mapping
logic.

Signed-off-by: Lorenzo Stoakes <lorenzo.stoa...@oracle.com>
---
 kernel/kcov.c | 42 ++++++++++++++++++++++++++----------------
 1 file changed, 26 insertions(+), 16 deletions(-)

diff --git a/kernel/kcov.c b/kernel/kcov.c
index 1d85597057e1..2bcf403e5f6f 100644
--- a/kernel/kcov.c
+++ b/kernel/kcov.c
@@ -484,31 +484,41 @@ void kcov_task_exit(struct task_struct *t)
        kcov_put(kcov);
 }
 
-static int kcov_mmap(struct file *filep, struct vm_area_struct *vma)
+static int kcov_mmap_error(int err)
+{
+       pr_warn_once("kcov: vm_insert_page() failed\n");
+       return err;
+}
+
+static int kcov_mmap_prepare(struct vm_area_desc *desc)
 {
        int res = 0;
-       struct kcov *kcov = vma->vm_file->private_data;
-       unsigned long size, off;
-       struct page *page;
+       struct kcov *kcov = desc->file->private_data;
+       unsigned long size, nr_pages, i;
+       struct page **pages;
        unsigned long flags;
 
        spin_lock_irqsave(&kcov->lock, flags);
        size = kcov->size * sizeof(unsigned long);
-       if (kcov->area == NULL || vma->vm_pgoff != 0 ||
-           vma->vm_end - vma->vm_start != size) {
+       if (kcov->area == NULL || desc->pgoff != 0 ||
+           vma_desc_size(desc) != size) {
                res = -EINVAL;
                goto exit;
        }
        spin_unlock_irqrestore(&kcov->lock, flags);
-       vm_flags_set(vma, VM_DONTEXPAND);
-       for (off = 0; off < size; off += PAGE_SIZE) {
-               page = vmalloc_to_page(kcov->area + off);
-               res = vm_insert_page(vma, vma->vm_start + off, page);
-               if (res) {
-                       pr_warn_once("kcov: vm_insert_page() failed\n");
-                       return res;
-               }
-       }
+
+       desc->vm_flags |= VM_DONTEXPAND;
+       nr_pages = size >> PAGE_SHIFT;
+
+       pages = mmap_action_mixedmap_pages(&desc->action, desc->start,
+                                          nr_pages);
+       if (!pages)
+               return -ENOMEM;
+
+       for (i = 0; i < nr_pages; i++)
+               pages[i] = vmalloc_to_page(kcov->area + i * PAGE_SIZE);
+       desc->action.error_hook = kcov_mmap_error;
+
        return 0;
 exit:
        spin_unlock_irqrestore(&kcov->lock, flags);
@@ -761,7 +771,7 @@ static const struct file_operations kcov_fops = {
        .open           = kcov_open,
        .unlocked_ioctl = kcov_ioctl,
        .compat_ioctl   = kcov_ioctl,
-       .mmap           = kcov_mmap,
+       .mmap_prepare   = kcov_mmap_prepare,
        .release        = kcov_close,
 };
 
-- 
2.51.0