[RFC PATCH V4 06/17] x86/hyperv: decrypt VMBus pages for sev-snp enlightened guest

[Tianyu Lan <ltykernel@gmail.com>]

From: Tianyu Lan <tiala@microsoft.com>

VMBus post msg, synic event and message pages are shared
with hypervisor and so decrypt these pages in the sev-snp guest.

Signed-off-by: Tianyu Lan <tiala@microsoft.com>
---
Change since RFC V3:
       * Set encrypt page back in the hv_synic_free()

Change since RFC V2:
       * Fix error in the error code path and encrypt
       	 pages correctly when decryption failure happens.
---
 drivers/hv/hv.c | 42 +++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 41 insertions(+), 1 deletion(-)

diff --git a/drivers/hv/hv.c b/drivers/hv/hv.c
index 008234894d28..e09cea8f2f04 100644
--- a/drivers/hv/hv.c
+++ b/drivers/hv/hv.c
@@ -20,6 +20,7 @@
 #include <linux/interrupt.h>
 #include <clocksource/hyperv_timer.h>
 #include <asm/mshyperv.h>
+#include <linux/set_memory.h>
 #include "hyperv_vmbus.h"
 
 /* The one and only */
@@ -117,7 +118,7 @@ int hv_post_message(union hv_connection_id connection_id,
 
 int hv_synic_alloc(void)
 {
-	int cpu;
+	int cpu, ret;
 	struct hv_per_cpu_context *hv_cpu;
 
 	/*
@@ -168,9 +169,39 @@ int hv_synic_alloc(void)
 			pr_err("Unable to allocate post msg page\n");
 			goto err;
 		}
+
+		if (hv_isolation_type_en_snp()) {
+			ret = set_memory_decrypted((unsigned long)
+				hv_cpu->synic_message_page, 1);
+			if (ret)
+				goto err;
+
+			ret = set_memory_decrypted((unsigned long)
+				hv_cpu->synic_event_page, 1);
+			if (ret)
+				goto err_decrypt_event_page;
+
+			ret = set_memory_decrypted((unsigned long)
+				hv_cpu->post_msg_page, 1);
+			if (ret)
+				goto err_decrypt_msg_page;
+
+			memset(hv_cpu->synic_message_page, 0, PAGE_SIZE);
+			memset(hv_cpu->synic_event_page, 0, PAGE_SIZE);
+			memset(hv_cpu->post_msg_page, 0, PAGE_SIZE);
+		}
 	}
 
 	return 0;
+
+err_decrypt_msg_page:
+	set_memory_encrypted((unsigned long)
+		hv_cpu->synic_event_page, 1);
+
+err_decrypt_event_page:
+	set_memory_encrypted((unsigned long)
+		hv_cpu->synic_message_page, 1);
+
 err:
 	/*
 	 * Any memory allocations that succeeded will be freed when
@@ -191,6 +222,15 @@ 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);
+
+		if (hv_isolation_type_en_snp()) {
+			set_memory_encrypted((unsigned long)
+				hv_cpu->synic_message_page, 1);
+			set_memory_encrypted((unsigned long)
+				hv_cpu->synic_event_page, 1);
+			set_memory_encrypted((unsigned long)
+				hv_cpu->post_msg_page, 1);
+		}
 	}
 
 	kfree(hv_context.hv_numa_map);
-- 
2.25.1