[PATCH v3 1/3] xen/privcmd: Corrected error handling path

[Souptick Joarder <jrdr.linux@xxxxxxxxx>]

Previously, if lock_pages() end up partially mapping pages, it used
to return -ERRNO due to which unlock_pages() have to go through
each pages[i] till *nr_pages* to validate them. This can be avoided
by passing correct number of partially mapped pages & -ERRNO separately,
while returning from lock_pages() due to error.

With this fix unlock_pages() doesn't need to validate pages[i] till
*nr_pages* for error scenario and few condition checks can be ignored.

Signed-off-by: Souptick Joarder <jrdr.linux@xxxxxxxxx>
Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: Paul Durrant <xadimgnik@xxxxxxxxx>
---
 drivers/xen/privcmd.c | 31 +++++++++++++++----------------
 1 file changed, 15 insertions(+), 16 deletions(-)

diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
index 5dfc59f..b001673 100644
--- a/drivers/xen/privcmd.c
+++ b/drivers/xen/privcmd.c
@@ -579,13 +579,13 @@ static long privcmd_ioctl_mmap_batch(
 
 static int lock_pages(
        struct privcmd_dm_op_buf kbufs[], unsigned int num,
-       struct page *pages[], unsigned int nr_pages)
+       struct page *pages[], unsigned int nr_pages, unsigned int *pinned)
 {
        unsigned int i;
 
        for (i = 0; i < num; i++) {
                unsigned int requested;
-               int pinned;
+               int page_count;
 
                requested = DIV_ROUND_UP(
                        offset_in_page(kbufs[i].uptr) + kbufs[i].size,
@@ -593,14 +593,15 @@ static int lock_pages(
                if (requested > nr_pages)
                        return -ENOSPC;
 
-               pinned = get_user_pages_fast(
+               page_count = get_user_pages_fast(
                        (unsigned long) kbufs[i].uptr,
                        requested, FOLL_WRITE, pages);
-               if (pinned < 0)
-                       return pinned;
+               if (page_count < 0)
+                       return page_count;
 
-               nr_pages -= pinned;
-               pages += pinned;
+               *pinned += page_count;
+               nr_pages -= page_count;
+               pages += page_count;
        }
 
        return 0;
@@ -610,13 +611,8 @@ static void unlock_pages(struct page *pages[], unsigned 
int nr_pages)
 {
        unsigned int i;
 
-       if (!pages)
-               return;
-
-       for (i = 0; i < nr_pages; i++) {
-               if (pages[i])
-                       put_page(pages[i]);
-       }
+       for (i = 0; i < nr_pages; i++)
+               put_page(pages[i]);
 }
 
 static long privcmd_ioctl_dm_op(struct file *file, void __user *udata)
@@ -629,6 +625,7 @@ static long privcmd_ioctl_dm_op(struct file *file, void 
__user *udata)
        struct xen_dm_op_buf *xbufs = NULL;
        unsigned int i;
        long rc;
+       unsigned int pinned = 0;
 
        if (copy_from_user(&kdata, udata, sizeof(kdata)))
                return -EFAULT;
@@ -682,9 +679,11 @@ static long privcmd_ioctl_dm_op(struct file *file, void 
__user *udata)
                goto out;
        }
 
-       rc = lock_pages(kbufs, kdata.num, pages, nr_pages);
-       if (rc)
+       rc = lock_pages(kbufs, kdata.num, pages, nr_pages, &pinned);
+       if (rc < 0) {
+               nr_pages = pinned;
                goto out;
+       }
 
        for (i = 0; i < kdata.num; i++) {
                set_xen_guest_handle(xbufs[i].h, kbufs[i].uptr);
-- 
1.9.1