[RFC PATCH 0/2] hv_netvsc: Fix shutdown regression on Win2012 hosts

[Mohammed Gamal <mgamal@redhat.com>]

Commit 0cf737808ae7 ("hv_netvsc: netvsc_teardown_gpadl() split") introduced
a regression that caused VMs not to shutdown after netvsc_device_remove() is
called. This is caused by GPADL teardown sequence change, and while that was 
necessary to fix issues with Win2016 hosts, it did introduce a regression for
earlier versions.

Prior to commit 0cf737808 the call sequence in netvsc_device_remove() was as 
follows (as implemented in netvsc_destroy_buf()):
1- Send NVSP_MSG1_TYPE_REVOKE_RECV_BUF message
2- Teardown receive buffer GPADL
3- Send NVSP_MSG1_TYPE_REVOKE_SEND_BUF message
4- Teardown send buffer GPADL
5- Close vmbus

This didn't work for WS2016 hosts. Commit 0cf737808 split netvsc_destroy_buf()
into two functions and rearranged the order as follows
1- Send NVSP_MSG1_TYPE_REVOKE_RECV_BUF message
2- Send NVSP_MSG1_TYPE_REVOKE_SEND_BUF message
3- Close vmbus
4- Teardown receive buffer GPADL
5- Teardown send buffer GPADL

That worked well for WS2016 hosts, but for WS2012 hosts it prevented VMs from
shutting down. 

This patch series works around this problem. The first patch splits
netvsc_revoke_buf() and netvsc_teardown_gpadl() into two finer grained
functions for tearing down send and receive buffers individally. The second patch
uses the finer grained functions to implement the teardown sequence according to
the host's version. We keep the behavior introduced in 0cf737808ae7 for Windows
2016 hosts, while we re-introduce the old sequence for earlier verions.

Mohammed Gamal (2):
  hv_netvsc: Split netvsc_revoke_buf() and netvsc_teardown_gpadl()
  hv_netvsc: Change GPADL teardown order according to Hyper-V version

 drivers/net/hyperv/netvsc.c | 50 +++++++++++++++++++++++++++++++++++++--------
 1 file changed, 42 insertions(+), 8 deletions(-)

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1.8.3.1