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Drivers: hv: vmbus: Fix ring buffer signaling

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Fix bugs in signaling the Hyper-V host when freeing space in the
host->guest ring buffer:

1. The interrupt_mask must not be used to determine whether to signal
   on the host->guest ring buffer
2. The ring buffer write_index must be read (via hv_get_bytes_to_write)
   *after* pending_send_sz is read in order to avoid a race condition
3. Comparisons with pending_send_sz must treat the "equals" case as
   not-enough-space
4. Don't signal if the pending_send_sz feature is not present. Older
   versions of Hyper-V that don't implement this feature will poll.

Fixes: 03bad714a1 ("vmbus: more host signalling avoidance")

Cc: Stable <stable@vger.kernel.org> # 4.14 and above
Signed-off-by: Michael Kelley <mhkelley@outlook.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Michael Kelley 2018-03-04 22:24:08 -07:00 • committed by Greg Kroah-Hartman
parent 661e50bc85
commit 655296c8bb
1 changed files with 35 additions and 17 deletions
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40
drivers/hv/ring_buffer.c
View file

@ -417,13 +417,24 @@ __hv_pkt_iter_next(struct vmbus_channel *channel,
} }
EXPORT_SYMBOL_GPL(__hv_pkt_iter_next); EXPORT_SYMBOL_GPL(__hv_pkt_iter_next);
/* How many bytes were read in this iterator cycle */
static u32 hv_pkt_iter_bytes_read(const struct hv_ring_buffer_info *rbi,
u32 start_read_index)
{
if (rbi->priv_read_index >= start_read_index)
return rbi->priv_read_index - start_read_index;
else
return rbi->ring_datasize - start_read_index +
rbi->priv_read_index;
}
/* /*
* Update host ring buffer after iterating over packets. * Update host ring buffer after iterating over packets.
*/ */
void hv_pkt_iter_close(struct vmbus_channel *channel) void hv_pkt_iter_close(struct vmbus_channel *channel)
{ {
struct hv_ring_buffer_info *rbi = &channel->inbound; struct hv_ring_buffer_info *rbi = &channel->inbound;
u32 orig_write_sz = hv_get_bytes_to_write(rbi); u32 curr_write_sz, pending_sz, bytes_read, start_read_index;
/* /*
* Make sure all reads are done before we update the read index since * Make sure all reads are done before we update the read index since
@ -431,8 +442,12 @@ void hv_pkt_iter_close(struct vmbus_channel *channel)
* is updated. * is updated.
*/ */
virt_rmb(); virt_rmb();
start_read_index = rbi->ring_buffer->read_index;
rbi->ring_buffer->read_index = rbi->priv_read_index; rbi->ring_buffer->read_index = rbi->priv_read_index;
if (!rbi->ring_buffer->feature_bits.feat_pending_send_sz)
return;
/* /*
* Issue a full memory barrier before making the signaling decision. * Issue a full memory barrier before making the signaling decision.
* Here is the reason for having this barrier: * Here is the reason for having this barrier:
@ -446,26 +461,29 @@ void hv_pkt_iter_close(struct vmbus_channel *channel)
*/ */
virt_mb(); virt_mb();
/* If host has disabled notifications then skip */ pending_sz = READ_ONCE(rbi->ring_buffer->pending_send_sz);
if (rbi->ring_buffer->interrupt_mask) if (!pending_sz)
return; return;
if (rbi->ring_buffer->feature_bits.feat_pending_send_sz) { /*
u32 pending_sz = READ_ONCE(rbi->ring_buffer->pending_send_sz); * Ensure the read of write_index in hv_get_bytes_to_write()
* happens after the read of pending_send_sz.
*/
virt_rmb();
curr_write_sz = hv_get_bytes_to_write(rbi);
bytes_read = hv_pkt_iter_bytes_read(rbi, start_read_index);
/* /*
* If there was space before we began iteration, * If there was space before we began iteration,
* then host was not blocked. Also handles case where * then host was not blocked.
* pending_sz is zero then host has nothing pending
* and does not need to be signaled.
*/ */
if (orig_write_sz > pending_sz)
if (curr_write_sz - bytes_read > pending_sz)
return; return;
/* If pending write will not fit, don't give false hope. */ /* If pending write will not fit, don't give false hope. */
if (hv_get_bytes_to_write(rbi) < pending_sz) if (curr_write_sz <= pending_sz)
return; return;
}
vmbus_setevent(channel); vmbus_setevent(channel);
} }