linux-kernel - [PATCH v2 2/5] Drivers: hv: allocate the exact needed memory for messages

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Date:   Mon,  6 Apr 2020 12:41:51 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     linux-hyperv@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Wei Liu <wei.liu@...nel.org>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        Michael Kelley <mikelley@...rosoft.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "Andrea Parri (Microsoft)" <parri.andrea@...il.com>
Subject: [PATCH v2 2/5] Drivers: hv: allocate the exact needed memory for messages

When we need to pass a buffer with Hyper-V message we don't need to always
allocate 256 bytes for the message: the real message length is known from
the header. Change 'struct onmessage_work_context' to make it possible to
not over-allocate.

Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
Reviewed-by: Michael Kelley <mikelley@...rosoft.com>
---
 drivers/hv/vmbus_drv.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 943b23beb992..b114bb411d7e 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -991,7 +991,10 @@ static struct bus_type  hv_bus = {
 
 struct onmessage_work_context {
 	struct work_struct work;
-	struct hv_message msg;
+	struct {
+		struct hv_message_header header;
+		u8 payload[];
+	} msg;
 };
 
 static void vmbus_onmessage_work(struct work_struct *work)
@@ -1044,7 +1047,8 @@ void vmbus_on_msg_dpc(unsigned long data)
 		goto msg_handled;
 
 	if (entry->handler_type	== VMHT_BLOCKING) {
-		ctx = kmalloc(sizeof(*ctx), GFP_ATOMIC);
+		ctx = kmalloc(sizeof(*ctx) + msg->header.payload_size,
+			      GFP_ATOMIC);
 		if (ctx == NULL)
 			return;
 
@@ -1098,10 +1102,11 @@ static void vmbus_force_channel_rescinded(struct vmbus_channel *channel)
 	WARN_ON(!is_hvsock_channel(channel));
 
 	/*
-	 * sizeof(*ctx) is small and the allocation should really not fail,
+	 * Allocation size is small and the allocation should really not fail,
 	 * otherwise the state of the hv_sock connections ends up in limbo.
 	 */
-	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL | __GFP_NOFAIL);
+	ctx = kzalloc(sizeof(*ctx) + sizeof(*rescind),
+		      GFP_KERNEL | __GFP_NOFAIL);
 
 	/*
 	 * So far, these are not really used by Linux. Just set them to the
@@ -1111,7 +1116,7 @@ static void vmbus_force_channel_rescinded(struct vmbus_channel *channel)
 	ctx->msg.header.payload_size = sizeof(*rescind);
 
 	/* These values are actually used by Linux. */
-	rescind = (struct vmbus_channel_rescind_offer *)ctx->msg.u.payload;
+	rescind = (struct vmbus_channel_rescind_offer *)ctx->msg.payload;
 	rescind->header.msgtype = CHANNELMSG_RESCIND_CHANNELOFFER;
 	rescind->child_relid = channel->offermsg.child_relid;
 
-- 
2.25.1