[PATCH 16/16] kcov: update kcov to use mmap_prepare, mmap_complete

[Lorenzo Stoakes]

Now we have the capacity to set up the VMA in f_op->mmap_prepare and then
later, once the VMA is established, insert a mixed mapping in
f_op->mmap_complete, do so for kcov.

We utilise the context desc->mmap_context field to pass context between
mmap_prepare and mmap_complete to conveniently provide the size over which
the mapping is performed.

Also note that we intentionally set VM_MIXEDMAP ahead of time so upon
mmap_complete being invoked, vm_insert_page() does not adjust VMA flags.

Signed-off-by: Lorenzo Stoakes <lorenzo.stoa...@oracle.com>
---
 kernel/kcov.c | 40 ++++++++++++++++++++++++++++------------
 1 file changed, 28 insertions(+), 12 deletions(-)

diff --git a/kernel/kcov.c b/kernel/kcov.c
index 1d85597057e1..53c8bcae54d0 100644
--- a/kernel/kcov.c
+++ b/kernel/kcov.c
@@ -484,23 +484,40 @@ 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_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;
        unsigned long flags;
+       int res = 0;
 
        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);
+
+       desc->vm_flags |= VM_DONTEXPAND | VM_MIXEDMAP;
+       desc->mmap_context = (void *)size;
+
+       return 0;
+exit:
+       spin_unlock_irqrestore(&kcov->lock, flags);
+       return res;
+}
+
+static int kcov_mmap_complete(struct file *file, struct vm_area_struct *vma,
+                              const void *context)
+{
+       struct kcov *kcov = file->private_data;
+       unsigned long size = (unsigned long)context;
+       struct page *page;
+       unsigned long off;
+       int res;
+
        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);
@@ -509,10 +526,8 @@ static int kcov_mmap(struct file *filep, struct 
vm_area_struct *vma)
                        return res;
                }
        }
+
        return 0;
-exit:
-       spin_unlock_irqrestore(&kcov->lock, flags);
-       return res;
 }
 
 static int kcov_open(struct inode *inode, struct file *filep)
@@ -761,7 +776,8 @@ 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,
+       .mmap_complete  = kcov_mmap_complete,
        .release        = kcov_close,
 };
 
-- 
2.51.0