[hyperv] Cope with Windows Server 2016 enlightenments

An "enlightened" external bootloader (such as Windows Server 2016's
winload.exe) may take ownership of the Hyper-V connection before all
INT 13 operations have been completed.  When this happens, all VMBus
devices are implicitly closed and we are left with a non-functional
network connection.

Detect when our Hyper-V connection has been lost (by checking the
SynIC message page MSR).  Reclaim ownership of the Hyper-V connection
and reestablish any VMBus devices, without disrupting any existing
iPXE state (such as IPv4 settings attached to the network device).

Windows Server 2016 will not cleanly take ownership of an active
Hyper-V connection.  Experimentation shows that we can quiesce by
resetting only the SynIC message page MSR; this results in a
successful SAN boot (on a Windows 2012 R2 physical host).  Choose to
quiesce by resetting (almost) all MSRs, in the hope that this will be
more robust against corner cases such as a stray synthetic interrupt
occurring during the handover.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

1 files changed, 15 insertions, 0 deletions

diff --git a/src/drivers/net/netvsc.h b/src/drivers/net/netvsc.h
index 39eeb891..93192357 100644
--- a/src/drivers/net/netvsc.h
+++ b/src/drivers/net/netvsc.h
@@ -362,4 +362,19 @@ struct netvsc_device {
 	int wait_rc;
 };
 
+/**
+ * Check if NetVSC device is obsolete
+ *
+ * @v netvsc		NetVSC device
+ * @v is_obsolete	NetVSC device is obsolete
+ *
+ * Check if NetVSC device is obsolete (i.e. was opened before the most
+ * recent Hyper-V reset).
+ */
+static inline __attribute__ (( always_inline )) int
+netvsc_is_obsolete ( struct netvsc_device *netvsc ) {
+
+	return vmbus_gpadl_is_obsolete ( netvsc->rx.gpadl );
+}
+
 #endif /* _NETVSC_H */