linux-kernel - [PATCH v2] pvcalls-front: 64-bit align flags

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Date:   Wed, 28 Feb 2018 18:05:34 -0800 (PST)
From:   Stefano Stabellini <sstabellini@...nel.org>
To:     jgross@...e.com, boris.ostrovsky@...cle.com
cc:     sstabellini@...nel.org, xen-devel@...ts.xenproject.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2] pvcalls-front: 64-bit align flags

We are using test_and_* operations on the status and flag fields of
struct sock_mapping. However, these functions require the operand to be
64-bit aligned on arm64. Currently, only status is 64-bit aligned.

Make status and flags explicitly 64-bit aligned.

Signed-off-by: Stefano Stabellini <stefano@...reto.com>

---
Changes in v2:
- use __attribute__((aligned(8)))
- add comments

diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c
index ca5b773..582929e 100644
--- a/drivers/xen/pvcalls-front.c
+++ b/drivers/xen/pvcalls-front.c
@@ -73,20 +73,25 @@ struct sock_mapping {
 			wait_queue_head_t inflight_conn_req;
 		} active;
 		struct {
-		/* Socket status */
+		/*
+		 * Socket status, needs to be 64-bit aligned due to the
+		 * test_and_* functions which have this requirement on arm64.
+		 */
 #define PVCALLS_STATUS_UNINITALIZED  0
 #define PVCALLS_STATUS_BIND          1
 #define PVCALLS_STATUS_LISTEN        2
-			uint8_t status;
+			uint8_t status __attribute__((aligned(8)));
 		/*
 		 * Internal state-machine flags.
 		 * Only one accept operation can be inflight for a socket.
 		 * Only one poll operation can be inflight for a given socket.
+		 * flags needs to be 64-bit aligned due to the test_and_*
+		 * functions which have this requirement on arm64.
 		 */
 #define PVCALLS_FLAG_ACCEPT_INFLIGHT 0
 #define PVCALLS_FLAG_POLL_INFLIGHT   1
 #define PVCALLS_FLAG_POLL_RET        2
-			uint8_t flags;
+			uint8_t flags __attribute__((aligned(8)));
 			uint32_t inflight_req_id;
 			struct sock_mapping *accept_map;
 			wait_queue_head_t inflight_accept_req;