[PATCH 2/3] kvm tools: check negative value of num_pages

[Liming Wang <walimisdev@gmail.com>]

If num_pages is negative, balloon will make kernel crash with
"out of memory". So we check this value to avoid it to be negative.

Signed-off-by: Liming Wang <walimisdev@gmail.com>
---
 tools/kvm/virtio/balloon.c |    8 ++++++--
 1 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/tools/kvm/virtio/balloon.c b/tools/kvm/virtio/balloon.c
index 854d04b..941023e 100644
--- a/tools/kvm/virtio/balloon.c
+++ b/tools/kvm/virtio/balloon.c
@@ -220,10 +220,14 @@ static struct ioport_operations virtio_bln_io_ops = {
 
 static void handle_sigmem(int sig)
 {
-	if (sig == SIGKVMADDMEM)
+	if (sig == SIGKVMADDMEM) {
 		bdev.config.num_pages += 256;
-	else
+	} else {
+		if (bdev.config.num_pages < 256){
+			return;
+		}
 		bdev.config.num_pages -= 256;
+	}
 
 	/* Notify that the configuration space has changed */
 	bdev.isr = VIRTIO_PCI_ISR_CONFIG;
-- 
1.7.0.4