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.
* 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 essiential to guest monitoring.
Therefore instead of the entire hv_balloon driver, the balloon 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@xxxxxxxxx>
---
v1 --> v1.1:
* Use HV_HYP_PAGE_SIZE instead of hard coding 4096 as suggested by
Michael.
* Explicitly print out the disable message if a function is
disabled as suggested by Michael.
drivers/hv/hv_balloon.c | 36 ++++++++++++++++++++++++++++++++++--
1 file changed, 34 insertions(+), 2 deletions(-)
diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
index 062156b88a87..eee7402cfc02 100644
--- 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
--
2.33.0
