Drivers: hv: vmbus: Remove the per-CPU post_msg_page

The post_msg_page was introduced in 2014 in
commit b29ef354 ("Drivers: hv: vmbus: Cleanup hv_post_message()")

Commit 68bb7bfb ("X86/Hyper-V: Enable IPI enlightenments") introduced
the hyperv_pcpu_input_arg in 2018, which can be used in hv_post_message().

Remove post_msg_page to simplify the code a little bit.
Signed-off-by: Dexuan Cui <decui@microsoft.com>
Reviewed-by: Jinank Jain <jinankjain@linux.microsoft.com>
Link: https://lore.kernel.org/r/20230408213441.15472-1-decui@microsoft.comSigned-off-by: Wei Liu <wei.liu@kernel.org>

drivers/hv/hv.c

@@ -84,14 +84,15 @@ int hv_post_message(union hv_connection_id connection_id,
 		  void *payload, size_t payload_size)
 {
 	struct hv_input_post_message *aligned_msg;
-	struct hv_per_cpu_context *hv_cpu;
+	unsigned long flags;
 	u64 status;
 
 	if (payload_size > HV_MESSAGE_PAYLOAD_BYTE_COUNT)
 		return -EMSGSIZE;
 
-	hv_cpu = get_cpu_ptr(hv_context.cpu_context);
-	aligned_msg = hv_cpu->post_msg_page;
+	local_irq_save(flags);
+
+	aligned_msg = *this_cpu_ptr(hyperv_pcpu_input_arg);
 	aligned_msg->connectionid = connection_id;
 	aligned_msg->reserved = 0;
 	aligned_msg->message_type = message_type;
@@ -106,11 +107,7 @@ int hv_post_message(union hv_connection_id connection_id,
 		status = hv_do_hypercall(HVCALL_POST_MESSAGE,
 				aligned_msg, NULL);
 
-	/* Preemption must remain disabled until after the hypercall
-	 * so some other thread can't get scheduled onto this cpu and
-	 * corrupt the per-cpu post_msg_page
-	 */
-	put_cpu_ptr(hv_cpu);
+	local_irq_restore(flags);
 
 	return hv_result(status);
 }
@@ -162,12 +159,6 @@ int hv_synic_alloc(void)
 				goto err;
 			}
 		}
-
-		hv_cpu->post_msg_page = (void *)get_zeroed_page(GFP_ATOMIC);
-		if (hv_cpu->post_msg_page == NULL) {
-			pr_err("Unable to allocate post msg page\n");
-			goto err;
-		}
 	}
 
 	return 0;
@@ -190,7 +181,6 @@ void hv_synic_free(void)
 
 		free_page((unsigned long)hv_cpu->synic_event_page);
 		free_page((unsigned long)hv_cpu->synic_message_page);
-		free_page((unsigned long)hv_cpu->post_msg_page);
 	}
 
 	kfree(hv_context.hv_numa_map);

drivers/hv/hyperv_vmbus.h

@@ -122,10 +122,6 @@ enum {
 struct hv_per_cpu_context {
 	void *synic_message_page;
 	void *synic_event_page;
-	/*
-	 * buffer to post messages to the host.
-	 */
-	void *post_msg_page;
 
 	/*
 	 * Starting with win8, we can take channel interrupts on any CPU;