linux-kernel - Issue with KVM under 4.10 and above

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Date:   Wed, 6 Dec 2017 21:19:29 -0500
From:   Wakko Warner <wakko@...mx.eu.org>
To:     linux-kernel@...r.kernel.org
Subject: Issue with KVM under 4.10 and above

Starting with 4.10-rc1, I'm seeing an issue with a VM that boots an old
kernel.  The VM uses kernel 3.3.0 and is booted directly by qemu.  This VM
is a copy of a physical machine.

During boot, it hangs for several seconds on "Using IPI No-Shortcut mode". 
The next line shows something about ata5 link down.  According to the kernel
timing, the difference is less than .3 seconds, however many seconds had
actually passed.  During boot, after fsck finishes, nothing happens, it's
like it's hung.  When I issue "sleep 1", it takes way longer than 1 second
to complete.

I made a copy of another system that has an old kernel (2.6.36.2).  It
boots, but it hangs for a few seconds after TCP cubic registered then prints
ata4 link down.  Issueing "sleep 1" takes a long time.  I also noticed that
issueing date several times shows the same date each time, even several
minutes later.

This worked with 4.9.65 and 67 (and older).

If I change the qemu command line to not use KVM, it works fine, although
it runs slower.

I tested some other VMs that use newer kernels (like 4.4.4).  They work OK.
with the host being 4.10.  I tested linuxmint 18.1 without problems. 
Issueing date several times shows the time incrementing as expected.

-- 
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 million bugs.