mshv: Ignore second stats page map result failure

Older versions of the hypervisor do not have a concept of separate SELF
and PARENT stats areas. In this case, mapping the HV_STATS_AREA_SELF page
is sufficient - it's the only page and it contains all available stats.

Mapping HV_STATS_AREA_PARENT returns HV_STATUS_INVALID_PARAMETER which
currently causes module init to fail on older hypevisor versions.

Detect this case and gracefully fall back to populating
stats_pages[HV_STATS_AREA_PARENT] with the already-mapped SELF page.

Add comments to clarify the behavior, including a clarification of why
this isn't needed for hv_call_map_stats_page2() which always supports
PARENT and SELF areas.

Signed-off-by: Purna Pavan Chandra Aekkaladevi <paekkaladevi@linux.microsoft.com>
Signed-off-by: Nuno Das Neves <nunodasneves@linux.microsoft.com>
Reviewed-by: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>
Acked-by: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>
Reviewed-by: Michael Kelley <mhklinux@outlook.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>

diff --git a/drivers/hv/mshv_root_hv_call.c b/drivers/hv/mshv_root_hv_call.c
index 598eaff4ff2994cba14e3a145b69800c8103507f..1f93b94d7580c372584d73c83a22bc3e1593acf3 100644 (file)
--- a/drivers/hv/mshv_root_hv_call.c
+++ b/drivers/hv/mshv_root_hv_call.c
@@ -813,6 +813,13 @@ hv_call_notify_port_ring_empty(u32 sint_index)
        return hv_result_to_errno(status);
 }
 
+/*
+ * Equivalent of hv_call_map_stats_page() for cases when the caller provides
+ * the map location.
+ *
+ * NOTE: This is a newer hypercall that always supports SELF and PARENT stats
+ * areas, unlike hv_call_map_stats_page().
+ */
 static int hv_call_map_stats_page2(enum hv_stats_object_type type,
                                   const union hv_stats_object_identity *identity,
                                   u64 map_location)
@@ -855,6 +862,34 @@ static int hv_call_map_stats_page2(enum hv_stats_object_type type,
        return ret;
 }
 
+static int
+hv_stats_get_area_type(enum hv_stats_object_type type,
+                      const union hv_stats_object_identity *identity)
+{
+       switch (type) {
+       case HV_STATS_OBJECT_HYPERVISOR:
+               return identity->hv.stats_area_type;
+       case HV_STATS_OBJECT_LOGICAL_PROCESSOR:
+               return identity->lp.stats_area_type;
+       case HV_STATS_OBJECT_PARTITION:
+               return identity->partition.stats_area_type;
+       case HV_STATS_OBJECT_VP:
+               return identity->vp.stats_area_type;
+       }
+
+       return -EINVAL;
+}
+
+/*
+ * Map a stats page, where the page location is provided by the hypervisor.
+ *
+ * NOTE: The concept of separate SELF and PARENT stats areas does not exist on
+ * older hypervisor versions. All the available stats information can be found
+ * on the SELF page. When attempting to map the PARENT area on a hypervisor
+ * that doesn't support it, return "success" but with a NULL address. The
+ * caller should check for this case and instead fallback to the SELF area
+ * alone.
+ */
 static int hv_call_map_stats_page(enum hv_stats_object_type type,
                                  const union hv_stats_object_identity *identity,
                                  void **addr)
@@ -863,7 +898,7 @@ static int hv_call_map_stats_page(enum hv_stats_object_type type,
        struct hv_input_map_stats_page *input;
        struct hv_output_map_stats_page *output;
        u64 status, pfn;
-       int ret = 0;
+       int hv_status, ret = 0;
 
        do {
                local_irq_save(flags);
@@ -878,11 +913,20 @@ static int hv_call_map_stats_page(enum hv_stats_object_type type,
                pfn = output->map_location;
 
                local_irq_restore(flags);
-               if (hv_result(status) != HV_STATUS_INSUFFICIENT_MEMORY) {
-                       ret = hv_result_to_errno(status);
+
+               hv_status = hv_result(status);
+               if (hv_status != HV_STATUS_INSUFFICIENT_MEMORY) {
                        if (hv_result_success(status))
                                break;
-                       return ret;
+
+                       if (hv_stats_get_area_type(type, identity) == HV_STATS_AREA_PARENT &&
+                           hv_status == HV_STATUS_INVALID_PARAMETER) {
+                               *addr = NULL;
+                               return 0;
+                       }
+
+                       hv_status_debug(status, "\n");
+                       return hv_result_to_errno(status);
                }
 
                ret = hv_call_deposit_pages(NUMA_NO_NODE,

diff --git a/drivers/hv/mshv_root_main.c b/drivers/hv/mshv_root_main.c
index 681b58154d5eae89d6e59c98cee9758be8ebe35c..d3e8a66443ad63d9dd06ff669fe5dee82d274e4a 100644 (file)
--- a/drivers/hv/mshv_root_main.c
+++ b/drivers/hv/mshv_root_main.c
@@ -993,6 +993,9 @@ static int mshv_vp_stats_map(u64 partition_id, u32 vp_index,
        if (err)
                goto unmap_self;
 
+       if (!stats_pages[HV_STATS_AREA_PARENT])
+               stats_pages[HV_STATS_AREA_PARENT] = stats_pages[HV_STATS_AREA_SELF];
+
        return 0;
 
 unmap_self: