From: kys@exchange.microsoft.com
To: gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org,
        devel@linuxdriverproject.org, olaf@aepfle.de, apw@canonical.com,
        vkuznets@redhat.com, jasowang@redhat.com,
        leann.ogasawara@canonical.com
Cc: "K. Y. Srinivasan" <kys@microsoft.com>, <stable@vger.kernel.org>
Subject: [PATCH 1/5] Drivers: hv: vmbus: Raise retry/wait limits in vmbus_post_msg()
Date: Wed,  7 Dec 2016 01:16:24 -0800
Message-Id: <1481102188-4414-1-git-send-email-kys@exchange.microsoft.com>
In-Reply-To: <1481102113-4365-1-git-send-email-kys@exchange.microsoft.com>
References: <1481102113-4365-1-git-send-email-kys@exchange.microsoft.com>
Reply-To: kys@microsoft.com
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 7088
Lines: 189

From: Vitaly Kuznetsov <vkuznets@redhat.com>

DoS protection conditions were altered in WS2016 and now it's easy to get
-EAGAIN returned from vmbus_post_msg() (e.g. when we try changing MTU on a
netvsc device in a loop). All vmbus_post_msg() callers don't retry the
operation and we usually end up with a non-functional device or crash.

While host's DoS protection conditions are unknown to me my tests show that
it can take up to 10 seconds before the message is sent so doing udelay()
is not an option, we really need to sleep. Almost all vmbus_post_msg()
callers are ready to sleep but there is one special case:
vmbus_initiate_unload() which can be called from interrupt/NMI context and
we can't sleep there. I'm also not sure about the lonely
vmbus_send_tl_connect_request() which has no in-tree users but its external
users are most likely waiting for the host to reply so sleeping there is
also appropriate.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Cc: <stable@vger.kernel.org>
---
 drivers/hv/channel.c      |   17 +++++++++--------
 drivers/hv/channel_mgmt.c |   10 ++++++----
 drivers/hv/connection.c   |   17 ++++++++++++-----
 drivers/hv/hyperv_vmbus.h |    2 +-
 4 files changed, 28 insertions(+), 18 deletions(-)

diff --git a/drivers/hv/channel.c b/drivers/hv/channel.c
index 5fb4c6d..d5b8d9f 100644
--- a/drivers/hv/channel.c
+++ b/drivers/hv/channel.c
@@ -181,7 +181,7 @@ int vmbus_open(struct vmbus_channel *newchannel, u32 send_ringbuffer_size,
 	spin_unlock_irqrestore(&vmbus_connection.channelmsg_lock, flags);
 
 	ret = vmbus_post_msg(open_msg,
-			       sizeof(struct vmbus_channel_open_channel));
+			     sizeof(struct vmbus_channel_open_channel), true);
 
 	if (ret != 0) {
 		err = ret;
@@ -233,7 +233,7 @@ int vmbus_send_tl_connect_request(const uuid_le *shv_guest_servie_id,
 	conn_msg.guest_endpoint_id = *shv_guest_servie_id;
 	conn_msg.host_service_id = *shv_host_servie_id;
 
-	return vmbus_post_msg(&conn_msg, sizeof(conn_msg));
+	return vmbus_post_msg(&conn_msg, sizeof(conn_msg), true);
 }
 EXPORT_SYMBOL_GPL(vmbus_send_tl_connect_request);
 
@@ -419,7 +419,7 @@ int vmbus_establish_gpadl(struct vmbus_channel *channel, void *kbuffer,
 	spin_unlock_irqrestore(&vmbus_connection.channelmsg_lock, flags);
 
 	ret = vmbus_post_msg(gpadlmsg, msginfo->msgsize -
-			       sizeof(*msginfo));
+			     sizeof(*msginfo), true);
 	if (ret != 0)
 		goto cleanup;
 
@@ -433,8 +433,8 @@ int vmbus_establish_gpadl(struct vmbus_channel *channel, void *kbuffer,
 		gpadl_body->gpadl = next_gpadl_handle;
 
 		ret = vmbus_post_msg(gpadl_body,
-				     submsginfo->msgsize -
-				     sizeof(*submsginfo));
+				     submsginfo->msgsize - sizeof(*submsginfo),
+				     true);
 		if (ret != 0)
 			goto cleanup;
 
@@ -485,8 +485,8 @@ int vmbus_teardown_gpadl(struct vmbus_channel *channel, u32 gpadl_handle)
 	list_add_tail(&info->msglistentry,
 		      &vmbus_connection.chn_msg_list);
 	spin_unlock_irqrestore(&vmbus_connection.channelmsg_lock, flags);
-	ret = vmbus_post_msg(msg,
-			       sizeof(struct vmbus_channel_gpadl_teardown));
+	ret = vmbus_post_msg(msg, sizeof(struct vmbus_channel_gpadl_teardown),
+			     true);
 
 	if (ret)
 		goto post_msg_err;
@@ -557,7 +557,8 @@ static int vmbus_close_internal(struct vmbus_channel *channel)
 	msg->header.msgtype = CHANNELMSG_CLOSECHANNEL;
 	msg->child_relid = channel->offermsg.child_relid;
 
-	ret = vmbus_post_msg(msg, sizeof(struct vmbus_channel_close_channel));
+	ret = vmbus_post_msg(msg, sizeof(struct vmbus_channel_close_channel),
+			     true);
 
 	if (ret) {
 		pr_err("Close failed: close post msg return is %d\n", ret);
diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index 26b4192..b1e85d2 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -321,7 +321,8 @@ static void vmbus_release_relid(u32 relid)
 	memset(&msg, 0, sizeof(struct vmbus_channel_relid_released));
 	msg.child_relid = relid;
 	msg.header.msgtype = CHANNELMSG_RELID_RELEASED;
-	vmbus_post_msg(&msg, sizeof(struct vmbus_channel_relid_released));
+	vmbus_post_msg(&msg, sizeof(struct vmbus_channel_relid_released),
+		       true);
 }
 
 void hv_event_tasklet_disable(struct vmbus_channel *channel)
@@ -728,7 +729,8 @@ void vmbus_initiate_unload(bool crash)
 	init_completion(&vmbus_connection.unload_event);
 	memset(&hdr, 0, sizeof(struct vmbus_channel_message_header));
 	hdr.msgtype = CHANNELMSG_UNLOAD;
-	vmbus_post_msg(&hdr, sizeof(struct vmbus_channel_message_header));
+	vmbus_post_msg(&hdr, sizeof(struct vmbus_channel_message_header),
+		       !crash);
 
 	/*
 	 * vmbus_initiate_unload() is also called on crash and the crash can be
@@ -1116,8 +1118,8 @@ int vmbus_request_offers(void)
 	msg->msgtype = CHANNELMSG_REQUESTOFFERS;
 
 
-	ret = vmbus_post_msg(msg,
-			       sizeof(struct vmbus_channel_message_header));
+	ret = vmbus_post_msg(msg, sizeof(struct vmbus_channel_message_header),
+			     true);
 	if (ret != 0) {
 		pr_err("Unable to request offers - %d\n", ret);
 
diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
index 6ce8b87..9b72ebc 100644
--- a/drivers/hv/connection.c
+++ b/drivers/hv/connection.c
@@ -111,7 +111,8 @@ static int vmbus_negotiate_version(struct vmbus_channel_msginfo *msginfo,
 	spin_unlock_irqrestore(&vmbus_connection.channelmsg_lock, flags);
 
 	ret = vmbus_post_msg(msg,
-			       sizeof(struct vmbus_channel_initiate_contact));
+			     sizeof(struct vmbus_channel_initiate_contact),
+			     true);
 	if (ret != 0) {
 		spin_lock_irqsave(&vmbus_connection.channelmsg_lock, flags);
 		list_del(&msginfo->msglistentry);
@@ -435,7 +436,7 @@ void vmbus_on_event(unsigned long data)
 /*
  * vmbus_post_msg - Send a msg on the vmbus's message connection
  */
-int vmbus_post_msg(void *buffer, size_t buflen)
+int vmbus_post_msg(void *buffer, size_t buflen, bool can_sleep)
 {
 	union hv_connection_id conn_id;
 	int ret = 0;
@@ -450,7 +451,7 @@ int vmbus_post_msg(void *buffer, size_t buflen)
 	 * insufficient resources. Retry the operation a couple of
 	 * times before giving up.
 	 */
-	while (retries < 20) {
+	while (retries < 100) {
 		ret = hv_post_message(conn_id, 1, buffer, buflen);
 
 		switch (ret) {
@@ -473,8 +474,14 @@ int vmbus_post_msg(void *buffer, size_t buflen)
 		}
 
 		retries++;
-		udelay(usec);
-		if (usec < 2048)
+		if (can_sleep && usec > 1000)
+			msleep(usec / 1000);
+		else if (usec < MAX_UDELAY_MS * 1000)
+			udelay(usec);
+		else
+			mdelay(usec / 1000);
+
+		if (usec < 256000)
 			usec *= 2;
 	}
 	return ret;
diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h
index 0675b39..27982df 100644
--- a/drivers/hv/hyperv_vmbus.h
+++ b/drivers/hv/hyperv_vmbus.h
@@ -683,7 +683,7 @@ struct hv_device *vmbus_device_create(const uuid_le *type,
 int vmbus_connect(void);
 void vmbus_disconnect(void);
 
-int vmbus_post_msg(void *buffer, size_t buflen);
+int vmbus_post_msg(void *buffer, size_t buflen, bool can_sleep);
 
 void vmbus_on_event(unsigned long data);
 void vmbus_on_msg_dpc(unsigned long data);
-- 
1.7.4.1