Drivers: hv: vmbus: Cleanup hv_post_message()

Minimize failures in this function by pre-allocating the buffer
for posting messages. The hypercall for posting the message can fail
for a number of reasons:

        1. Transient resource related issues
        2. Buffer alignment
        3. Buffer cannot span a page boundry

We address issues 2 and 3 by preallocating a per-cpu page for the buffer.
Transient resource related failures are handled by retrying by the callers
of this function.

This patch is based on the investigation
done by Dexuan Cui <decui@microsoft.com>.

I would like to thank Sitsofe Wheeler <sitsofe@yahoo.com>
for reporting the issue and helping in debuggging.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Reported-by: Sitsofe Wheeler <sitsofe@yahoo.com>
Cc: <stable@vger.kernel.org>
Tested-by: Sitsofe Wheeler <sitsofe@yahoo.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

2 files changed, 19 insertions, 12 deletions

diff --git a/drivers/hv/hv.c b/drivers/hv/hv.c
index edfc8488cb03..3e4235c7a47f 100644
--- a/drivers/hv/hv.c
+++ b/drivers/hv/hv.c
@@ -138,6 +138,8 @@ int hv_init(void)
         memset(hv_context.synic_event_page, 0, sizeof(void *) * NR_CPUS);
         memset(hv_context.synic_message_page, 0,
                sizeof(void *) * NR_CPUS);
+        memset(hv_context.post_msg_page, 0,
+               sizeof(void *) * NR_CPUS);
         memset(hv_context.vp_index, 0,
                sizeof(int) * NR_CPUS);
         memset(hv_context.event_dpc, 0,
@@ -217,26 +219,18 @@ int hv_post_message(union hv_connection_id connection_id,
                   enum hv_message_type message_type,
                   void *payload, size_t payload_size)
 {
-        struct aligned_input {
-                u64 alignment8;
-                struct hv_input_post_message msg;
-        };
 
         struct hv_input_post_message *aligned_msg;
         u16 status;
-        unsigned long addr;
 
         if (payload_size > HV_MESSAGE_PAYLOAD_BYTE_COUNT)
                 return -EMSGSIZE;
 
-        addr = (unsigned long)kmalloc(sizeof(struct aligned_input), GFP_ATOMIC);
-        if (!addr)
-                return -ENOMEM;
-
         aligned_msg = (struct hv_input_post_message *)
-                        (ALIGN(addr, HV_HYPERCALL_PARAM_ALIGN));
+                        hv_context.post_msg_page[get_cpu()];
 
         aligned_msg->connectionid = connection_id;
+        aligned_msg->reserved = 0;
         aligned_msg->message_type = message_type;
         aligned_msg->payload_size = payload_size;
         memcpy((void *)aligned_msg->payload, payload, payload_size);
@@ -244,8 +238,7 @@ int hv_post_message(union hv_connection_id connection_id,
         status = do_hypercall(HVCALL_POST_MESSAGE, aligned_msg, NULL)
                 & 0xFFFF;
 
-        kfree((void *)addr);
-
+        put_cpu();
         return status;
 }
 
@@ -294,6 +287,14 @@ int hv_synic_alloc(void)
                         pr_err("Unable to allocate SYNIC event page\n");
                         goto err;
                 }
+
+                hv_context.post_msg_page[cpu] =
+                        (void *)get_zeroed_page(GFP_ATOMIC);
+
+                if (hv_context.post_msg_page[cpu] == NULL) {
+                        pr_err("Unable to allocate post msg page\n");
+                        goto err;
+                }
         }
 
         return 0;
@@ -308,6 +309,8 @@ static void hv_synic_free_cpu(int cpu)
                 free_page((unsigned long)hv_context.synic_event_page[cpu]);
         if (hv_context.synic_message_page[cpu])
                 free_page((unsigned long)hv_context.synic_message_page[cpu]);
+        if (hv_context.post_msg_page[cpu])
+                free_page((unsigned long)hv_context.post_msg_page[cpu]);
 }
 
 void hv_synic_free(void)
diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h
index 22b750749a39..c386d8dc7223 100644
--- a/drivers/hv/hyperv_vmbus.h
+++ b/drivers/hv/hyperv_vmbus.h
@@ -515,6 +515,10 @@ struct hv_context {
          * per-cpu list of the channels based on their CPU affinity.
          */
         struct list_head percpu_list[NR_CPUS];
+        /*
+         * buffer to post messages to the host.
+         */
+        void *post_msg_page[NR_CPUS];
 };
 
 extern struct hv_context hv_context;