If memory hot-add fails with the error -EEXIST, then this is a permanent
failure. Notify the host of this information, so the host will not attempt
hot-add again. If the failure were a transient failure, host will attempt
a hot-add after some delay.
In this version of the patch, I have added some additional comments
to clarify how the host treats different failure conditions.
Signed-off-by: K. Y. Srinivasan <kys@xxxxxxxxxxxxx>
---
drivers/hv/hv_balloon.c | 33 +++++++++++++++++++++++++++++++--
1 files changed, 31 insertions(+), 2 deletions(-)
diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
index 71655b4..4cc1d10 100644
--- a/drivers/hv/hv_balloon.c
+++ b/drivers/hv/hv_balloon.c
@@ -583,6 +583,16 @@ static void hv_mem_hot_add(unsigned long start, unsigned long size,
if (ret) {
pr_info("hot_add memory failed error is %d\n", ret);
+ if (ret == -EEXIST) {
+ /*
+ * This error indicates that the error
+ * is not a transient failure. This is the
+ * case where the guest's physical address map
+ * precludes hot adding memory. Stop all further
+ * memory hot-add.
+ */
+ do_hot_add = false;
+ }
has->ha_end_pfn -= HA_CHUNK;
has->covered_end_pfn -= processed_pfn;
break;
@@ -842,11 +852,30 @@ static void hot_add_req(struct work_struct *dummy)
rg_sz = region_size;
}
- resp.page_count = process_hot_add(pg_start, pfn_cnt,
- rg_start, rg_sz);
+ if (do_hot_add)
+ resp.page_count = process_hot_add(pg_start, pfn_cnt,
+ rg_start, rg_sz);
#endif
+ /*
+ * The result field of the response structure has the
+ * following semantics:
+ *
+ * 1. If all or some pages hot-added: Guest should return success.
+ *
+ * 2. If no pages could be hot-added:
+ *
+ * If the guest returns success, then the host
+ * will not attempt any further hot-add operations. This
+ * signifies a permanent failure.
+ *
+ * If the guest returns failure, then this failure will be
+ * treated as a transient failure and the host may retry the
+ * hot-add operation after some delay.
+ */
if (resp.page_count > 0)
resp.result = 1;
+ else if (!do_hot_add)
+ resp.result = 1;
else
resp.result = 0;
--
1.7.4.1
--
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