vmw_balloon: do not use 2MB without batching

BugLink: https://bugs.launchpad.net/bugs/1835972
commit 5081efd112560d3febb328e627176235b250d59d upstream.

If the hypervisor sets 2MB batching is on, while batching is cleared,
the balloon code breaks. In this case the legacy mechanism is used with
2MB page. The VM would report a 2MB page is ballooned, and the
hypervisor would only take the first 4KB.

While the hypervisor should not report such settings, make the code more
robust by not enabling 2MB support without batching.

Fixes: 365bd7ef7ec8e ("VMware balloon: Support 2m page ballooning.")
Cc: stable@vger.kernel.org
Reviewed-by: Xavier Deguillard <xdeguillard@vmware.com>
Signed-off-by: Nadav Amit <nadav.amit@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

diff --git a/drivers/misc/vmw_balloon.c b/drivers/misc/vmw_balloon.c
index f31b2f6fde2230cab83e90afb362a0fccf15eebc..4967cebddf48f11695e275f6da8904de41a49b90 100644 (file)
--- a/drivers/misc/vmw_balloon.c
+++ b/drivers/misc/vmw_balloon.c
@@ -341,7 +341,13 @@ static bool vmballoon_send_start(struct vmballoon *b, unsigned long req_caps)
                success = false;
        }
 
-       if (b->capabilities & VMW_BALLOON_BATCHED_2M_CMDS)
+       /*
+        * 2MB pages are only supported with batching. If batching is for some
+        * reason disabled, do not use 2MB pages, since otherwise the legacy
+        * mechanism is used with 2MB pages, causing a failure.
+        */
+       if ((b->capabilities & VMW_BALLOON_BATCHED_2M_CMDS) &&
+           (b->capabilities & VMW_BALLOON_BATCHED_CMDS))
                b->supported_page_sizes = 2;
        else
                b->supported_page_sizes = 1;