linux-kernel - [PATCH 4.4 18/47] vmw_balloon: do not use 2MB without batching

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Date:   Fri,  7 Sep 2018 23:10:14 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Xavier Deguillard <xdeguillard@...are.com>,
        Nadav Amit <nadav.amit@...il.com>
Subject: [PATCH 4.4 18/47] vmw_balloon: do not use 2MB without batching

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Nadav Amit <namit@...are.com>

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@...r.kernel.org
Reviewed-by: Xavier Deguillard <xdeguillard@...are.com>
Signed-off-by: Nadav Amit <nadav.amit@...il.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/misc/vmw_balloon.c |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

--- a/drivers/misc/vmw_balloon.c
+++ b/drivers/misc/vmw_balloon.c
@@ -341,7 +341,13 @@ static bool vmballoon_send_start(struct
 		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;