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FreeBSD-EN-17:03.hyperv                                         Errata Notice
                                                          The FreeBSD Project

Topic:          Compatibility with Hyper-V/storage after KB3172614 or
                KB3179574

Category:       core
Module:         hyperv/storvsc
Announced:      2017-02-23
Credits:        Microsoft OSTC
Affects:        FreeBSD 11.0-RELEASE
Corrected:      2016-10-19 07:43:39 UTC (stable/11, 11.0-STABLE)
                2017-02-23 07:11:48 UTC (releng/11.0, 11.0-RELEASE-p8)

For general information regarding FreeBSD Errata Notices and Security
Advisories, including descriptions of the fields above, security
branches, and the following sections, please visit
<URL:https://security.FreeBSD.org/>.

I.   Background

Hyper-V is a default hypervisor provided on Windows server by Microsoft.
ATA driver is the legacy storage driver for FreeBSD on Hyper-V, now they
are replaced by synthetic driver which has better performance. There are
issues when attaching synthetic storage driver for FreeBSD 11 on some of
Hyper-V hosts.

II.  Problem Description

There are some compatibility issues with the FreeBSD Hyper-V driver, 
which will cause the OS disk to be detached if August 2016 update rollup
is applied on Windows host (KB3172614 or KB3179574).

III. Impact

FreeBSD 11.0 can not be installed on a guest system on Hyper-V host.

IV.  Workaround

On Hyper-V connection, when the installer boot prompt, select

    3. Escape to the loader prompt

Then:

    set hw.ata.disk_enable=1
    boot.

Note: this workaround force FreeBSD to use legacy storage driver
which is much slower than synthetic driver.

V.   Solution

Perform one of the following:

1) Upgrade your system to a supported FreeBSD stable or release / security
branch (releng) dated after the correction date.

Afterward, reboot the system.

2) To update your system via a binary patch:

Systems running a RELEASE version of FreeBSD on the i386 or amd64
platforms can be updated via the freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install

Afterward, reboot the system.

3) To update your system via a source code patch:

The following patches have been verified to apply to the applicable
FreeBSD release branches.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

# fetch https://security.FreeBSD.org/patches/EN-17:03/hyperv.patch
# fetch https://security.FreeBSD.org/patches/EN-17:03/hyperv.patch.asc
# gpg --verify hyperv.patch.asc

b) Apply the patch.  Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch

c) Recompile your kernel as described in
<URL:https://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
system.

VI.  Correction details

The following list contains the correction revision numbers for each
affected branch.

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/11/                                                        r307617
releng/11.0/                                                      r314125
- -------------------------------------------------------------------------

To see which files were modified by a particular revision, run the
following command, replacing NNNNNN with the revision number, on a
machine with Subversion installed:

# svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base

Or visit the following URL, replacing NNNNNN with the revision number:

<URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>

VII. References

<URL:https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=212721>

<URL:https://support.microsoft.com/en-au/help/24717/windows-8-1-and-windows-server-2012-r2-update-history>

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