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>
The (undocumented) VMBus protocol seems to allow for transfer
page-based packets where the data payload is split into an arbitrary
set of ranges within the transfer page set.
The RNDIS protocol includes a length field within the header of each
message, and it is known from observation that multiple RNDIS messages
can be concatenated into a single VMBus message.
iPXE currently assumes that the transfer page range boundaries are
entirely arbitrary, and uses the RNDIS header length to determine the
RNDIS message boundaries.
Windows Server 2012 R2 generates an RNDIS_INDICATE_STATUS_MSG for an
undocumented and unknown status code (0x40020006) with a malformed
RNDIS header length: the length does not cover the StatusBuffer
portion of the message. This causes iPXE to report a malformed RNDIS
message and to discard any further RNDIS messages within the same
VMBus message.
The Linux Hyper-V driver assumes that the transfer page range
boundaries correspond to RNDIS message boundaries, and so does not
notice the malformed length field in the RNDIS header.
Match the behaviour of the Linux Hyper-V driver: assume that the
transfer page range boundaries correspond to the RNDIS message
boundaries and ignore the RNDIS header length. This avoids triggering
the "malformed packet" error and also avoids unnecessary data copying:
since we now have one I/O buffer per RNDIS message, there is no longer
any need to use iob_split().
Signed-off-by: Michael Brown <mcb30@ipxe.org>
Allow for elision of transmitted TCP ACKs by handling all received
VMBus messages in each network device poll operation.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
On Windows Server 2012 R2, the receive buffer teardown completion
message seems to occasionally be deferred until after the VMBus
channel has been closed. This happens even if there are no packets
currently in the receive buffer.
Work around this problem by separating the revocation and teardown of
the receive buffer, and deferring the teardown until after the VMBus
channel has been closed.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
Michael Brown