This is a note to let you know that I've just added the patch titled
Drivers: hv: vmbus: finally fix hv_need_to_signal_on_read()
to my char-misc git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git
in the char-misc-linus branch.
The patch will show up in the next release of the linux-next tree
(usually sometime within the next 24 hours during the week.)
The patch will hopefully also be merged in Linus's tree for the
next -rc kernel release.
If you have any questions about this process, please let me know.
>From 433e19cf33d34bb6751c874a9c00980552fe508c Mon Sep 17 00:00:00 2001
From: Dexuan Cui <decui@xxxxxxxxxxxxx>
Date: Sat, 28 Jan 2017 11:46:02 -0700
Subject: Drivers: hv: vmbus: finally fix hv_need_to_signal_on_read()
Commit a389fcfd2cb5 ("Drivers: hv: vmbus: Fix signaling logic in
hv_need_to_signal_on_read()")
added the proper mb(), but removed the test "prev_write_sz < pending_sz"
when making the signal decision.
As a result, the guest can signal the host unnecessarily,
and then the host can throttle the guest because the host
thinks the guest is buggy or malicious; finally the user
running stress test can perceive intermittent freeze of
the guest.
This patch brings back the test, and properly handles the
in-place consumption APIs used by NetVSC (see get_next_pkt_raw(),
put_pkt_raw() and commit_rd_index()).
Fixes: a389fcfd2cb5 ("Drivers: hv: vmbus: Fix signaling logic in
hv_need_to_signal_on_read()")
Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
Reported-by: Rolf Neugebauer <rolf.neugebauer@xxxxxxxxxx>
Tested-by: Rolf Neugebauer <rolf.neugebauer@xxxxxxxxxx>
Cc: "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx>
Cc: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
Cc: Stephen Hemminger <sthemmin@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: K. Y. Srinivasan <kys@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/hv/ring_buffer.c | 1 +
drivers/net/hyperv/netvsc.c | 6 ++++++
include/linux/hyperv.h | 32 ++++++++++++++++++++++++++++++--
3 files changed, 37 insertions(+), 2 deletions(-)
diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c
index cd49cb17eb7f..308dbda700eb 100644
--- a/drivers/hv/ring_buffer.c
+++ b/drivers/hv/ring_buffer.c
@@ -383,6 +383,7 @@ int hv_ringbuffer_read(struct vmbus_channel *channel,
return ret;
}
+ init_cached_read_index(channel);
next_read_location = hv_get_next_read_location(inring_info);
next_read_location = hv_copyfrom_ringbuffer(inring_info, &desc,
sizeof(desc),
diff --git a/drivers/net/hyperv/netvsc.c b/drivers/net/hyperv/netvsc.c
index 5a1cc089acb7..86e5749226ef 100644
--- a/drivers/net/hyperv/netvsc.c
+++ b/drivers/net/hyperv/netvsc.c
@@ -1295,6 +1295,9 @@ void netvsc_channel_cb(void *context)
ndev = hv_get_drvdata(device);
buffer = get_per_channel_state(channel);
+ /* commit_rd_index() -> hv_signal_on_read() needs this. */
+ init_cached_read_index(channel);
+
do {
desc = get_next_pkt_raw(channel);
if (desc != NULL) {
@@ -1347,6 +1350,9 @@ void netvsc_channel_cb(void *context)
bufferlen = bytes_recvd;
}
+
+ init_cached_read_index(channel);
+
} while (1);
if (bufferlen > NETVSC_PACKET_SIZE)
diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index 42fe43fb0c80..183efde54269 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -128,6 +128,7 @@ struct hv_ring_buffer_info {
u32 ring_data_startoffset;
u32 priv_write_index;
u32 priv_read_index;
+ u32 cached_read_index;
};
/*
@@ -180,6 +181,19 @@ static inline u32 hv_get_bytes_to_write(struct hv_ring_buffer_info *rbi)
return write;
}
+static inline u32 hv_get_cached_bytes_to_write(
+ const struct hv_ring_buffer_info *rbi)
+{
+ u32 read_loc, write_loc, dsize, write;
+
+ dsize = rbi->ring_datasize;
+ read_loc = rbi->cached_read_index;
+ write_loc = rbi->ring_buffer->write_index;
+
+ write = write_loc >= read_loc ? dsize - (write_loc - read_loc) :
+ read_loc - write_loc;
+ return write;
+}
/*
* VMBUS version is 32 bit entity broken up into
* two 16 bit quantities: major_number. minor_number.
@@ -1488,7 +1502,7 @@ hv_get_ring_buffer(struct hv_ring_buffer_info *ring_info)
static inline void hv_signal_on_read(struct vmbus_channel *channel)
{
- u32 cur_write_sz;
+ u32 cur_write_sz, cached_write_sz;
u32 pending_sz;
struct hv_ring_buffer_info *rbi = &channel->inbound;
@@ -1512,12 +1526,24 @@ static inline void hv_signal_on_read(struct vmbus_channel *channel)
cur_write_sz = hv_get_bytes_to_write(rbi);
- if (cur_write_sz >= pending_sz)
+ if (cur_write_sz < pending_sz)
+ return;
+
+ cached_write_sz = hv_get_cached_bytes_to_write(rbi);
+ if (cached_write_sz < pending_sz)
vmbus_setevent(channel);
return;
}
+static inline void
+init_cached_read_index(struct vmbus_channel *channel)
+{
+ struct hv_ring_buffer_info *rbi = &channel->inbound;
+
+ rbi->cached_read_index = rbi->ring_buffer->read_index;
+}
+
/*
* An API to support in-place processing of incoming VMBUS packets.
*/
@@ -1569,6 +1595,8 @@ static inline void put_pkt_raw(struct vmbus_channel *channel,
* This call commits the read index and potentially signals the host.
* Here is the pattern for using the "in-place" consumption APIs:
*
+ * init_cached_read_index();
+ *
* while (get_next_pkt_raw() {
* process the packet "in-place";
* put_pkt_raw();
--
2.11.0
--
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