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FreeBSD-EN-21:23.virtio_blk                                     Errata Notice
                                                          The FreeBSD Project

Topic:          virtio_blk(4) fails to attach on some hypervisors

Category:       core
Module:         virtio_blk
Announced:      2021-08-24
Affects:        FreeBSD 13.0
Corrected:      2021-06-28 15:16:29 UTC (stable/13, 13.0-STABLE)
                2021-08-24 16:36:55 UTC (releng/13.0, 13.0-RELEASE-p4)

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Advisories, including descriptions of the fields above, security
branches, and the following sections, please visit

I.   Background

VirtIO is a specification for para-virtualized I/O in a virtual machine
(VM).  It defines an interface for efficient I/O between the hypervisor
and VM. virtio_blk(4) is a driver handling VirtIO block devices.

II.  Problem Description

The virtio_blk(4) driver sends commands to the host to query disk
identifiers before acknowledging to the host that the driver is ready.

III. Impact

Affected versions of FreeBSD will not boot under some hypervisors, or
under the presence of modern and non-transitional VirtIO block devices.

IV.  Workaround

No workaround is available.  FreeBSD running in QEMU emulator is not
affected by this issue.

V.   Solution

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

Perform one of the following:

1) To update your system via a binary patch:

Systems running a RELEASE version of FreeBSD on the amd64, i386, or
(on FreeBSD 13 and later) arm64 platforms can be updated via the
freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install
# shutdown -r +10min "Rebooting for an erratum update"

2) 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-21:23/virtio_blk.patch
# fetch https://security.FreeBSD.org/patches/EN-21:23/virtio_blk.patch.asc
# gpg --verify virtio_blk.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

VI.  Correction details

This issue is corrected by the corresponding Git commit hash or Subversion
revision number in the following stable and release branches:

Branch/path                             Hash                     Revision
- -------------------------------------------------------------------------
stable/13/                              6fd5a4a6f3ac    stable/13-n246114
releng/13.0/                            f66e34809906  releng/13.0-n244753
- -------------------------------------------------------------------------

Run the following command to see which files were modified by a
particular commit:

# git show --stat <commit hash>

Or visit the following URL, replacing NNNNNN with the hash:


To determine the commit count in a working tree (for comparison against
nNNNNNN in the table above), run:

# git rev-list --count --first-parent HEAD

VII. References

The latest revision of this advisory is available at

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