Drivers: hv: balloon: Disable balloon and hot-add accordingly

Currently there are known potential issues for balloon and hot-add on
ARM64:

*	Unballoon requests from Hyper-V should only unballoon ranges
	that are guest page size aligned, otherwise guests cannot handle
	because it's impossible to partially free a page. This is a
	problem when guest page size > 4096 bytes.

*	Memory hot-add requests from Hyper-V should provide the NUMA
	node id of the added ranges or ARM64 should have a functional
	memory_add_physaddr_to_nid(), otherwise the node id is missing
	for add_memory().

These issues require discussions on design and implementation. In the
meanwhile, post_status() is working and essential to guest monitoring.
Therefore instead of disabling the entire hv_balloon driver, the
ballooning (when page size > 4096 bytes) and hot-add are disabled
accordingly for now. Once the issues are fixed, they can be re-enable in
these cases.

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/20220325023212.1570049-3-boqun.feng@gmail.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>

diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
index 062156b..eee7402 100644 (file)
--- a/drivers/hv/hv_balloon.c
+++ b/drivers/hv/hv_balloon.c
@@ -1660,6 +1660,38 @@ static void disable_page_reporting(void)
        }
 }
 
+static int ballooning_enabled(void)
+{
+       /*
+        * Disable ballooning if the page size is not 4k (HV_HYP_PAGE_SIZE),
+        * since currently it's unclear to us whether an unballoon request can
+        * make sure all page ranges are guest page size aligned.
+        */
+       if (PAGE_SIZE != HV_HYP_PAGE_SIZE) {
+               pr_info("Ballooning disabled because page size is not 4096 bytes\n");
+               return 0;
+       }
+
+       return 1;
+}
+
+static int hot_add_enabled(void)
+{
+       /*
+        * Disable hot add on ARM64, because we currently rely on
+        * memory_add_physaddr_to_nid() to get a node id of a hot add range,
+        * however ARM64's memory_add_physaddr_to_nid() always return 0 and
+        * DM_MEM_HOT_ADD_REQUEST doesn't have the NUMA node information for
+        * add_memory().
+        */
+       if (IS_ENABLED(CONFIG_ARM64)) {
+               pr_info("Memory hot add disabled on ARM64\n");
+               return 0;
+       }
+
+       return 1;
+}
+
 static int balloon_connect_vsp(struct hv_device *dev)
 {
        struct dm_version_request version_req;
@@ -1731,8 +1763,8 @@ static int balloon_connect_vsp(struct hv_device *dev)
         * currently still requires the bits to be set, so we have to add code
         * to fail the host's hot-add and balloon up/down requests, if any.
         */
-       cap_msg.caps.cap_bits.balloon = 1;
-       cap_msg.caps.cap_bits.hot_add = 1;
+       cap_msg.caps.cap_bits.balloon = ballooning_enabled();
+       cap_msg.caps.cap_bits.hot_add = hot_add_enabled();
 
        /*
         * Specify our alignment requirements as it relates