VirtualBox 4.3.18 and AHCI

Update 2014-11-30

Upgrading to Oracle VirtualBox 4.3.20 removed the timeout messages shown below.

The bug was acknowledged in the change log as

Storage: fixed an interrupt acknowledge issue causing hanging guests or slower I/O (4.3.18
regression)

Since upgrading Oracle VirtualBox from 4.3.16 to 4.3.18 on my Windows 7 x64 host, most of my FreeBSD guests from time to time shows kernel messages like the ones below.

ahcich2: Timeout on slot 7 port 0
ahcich2: is 00000008 cs 00000000 ss 00000000 rs 00000080 tfd 50 serr 00000000 cmd 1000c717
(ada2:ahcich2:0:0:0): WRITE_FPDMA_QUEUED. ACB: 61 40 62 d4 9c 40 00 00 00 00 00 00
(ada2:ahcich2:0:0:0): CAM status: Command timeout
(ada2:ahcich2:0:0:0): Retrying command

It doesn’t matter if your FreeBSD guests run version 4.3.16 or version 4.3.18 of the emulators/virtualbox-ose-additions port.

Someone else reported similar kernel messages on physical servers, making me believe some recent changes in FreeBSD can be blamed. Or, maybe this is just a coincidence, despite the similarities.