Drivers: hv: hv_balloon: correctly handle val.freeram<num_pages case

'Drivers: hv: hv_balloon: refuse to balloon below the floor' fix does not
correctly handle the case when val.freeram < num_pages as val.freeram is
__kernel_ulong_t and the 'val.freeram - num_pages' value will be a huge
positive value instead of being negative.

Usually host doesn't ask us to balloon more than val.freeram but in case
he have a memory hog started after we post the last pressure report we
can get into troubles.

Suggested-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
index 74312c88534a2d55c6f0df5794b4508392965615..4052ad8255fa7bcc681a3ed5622147ae9de94965 100644 (file)
--- a/drivers/hv/hv_balloon.c
+++ b/drivers/hv/hv_balloon.c
@@ -1155,7 +1155,7 @@ static void balloon_up(struct work_struct *dummy)
        floor = compute_balloon_floor();
 
        /* Refuse to balloon below the floor, keep the 2M granularity. */
-       if (val.freeram - num_pages < floor) {
+       if (val.freeram < num_pages || val.freeram - num_pages < floor) {
                num_pages = val.freeram > floor ? (val.freeram - floor) : 0;
                num_pages -= num_pages % PAGES_IN_2M;
        }