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Commit53fafdbb8b("KVM: x86: switch KVMCLOCK base to monotonic raw clock") changed kvmclock to use tkr_raw instead of tkr_mono. However, the default kvmclock_offset for the VM was still based on the monotonic clock and, if the raw clock drifted enough from the monotonic clock, this could cause a negative system_time to be written to the guest's struct pvclock. RHEL5 does not like it and (if it boots fast enough to observe a negative time value) it hangs. There is another thing to be careful about: getboottime64 returns the host boot time with tkr_mono frequency, and subtracting the tkr_raw-based kvmclock value will cause the wallclock to be off if tkr_raw drifts from tkr_mono. To avoid this, compute the wallclock delta from the current time instead of being clever and using getboottime64. Fixes:53fafdbb8b("KVM: x86: switch KVMCLOCK base to monotonic raw clock") Cc: stable@vger.kernel.org Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.