Re: [PATCH] KVM: x86/xen: Do not corrupt KVM clock in kvm_xen_shared_info_init()

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On Sun, Apr 07, 2024, David Woodhouse wrote:
> From: David Woodhouse <dwmw@xxxxxxxxxxxx>
> The KVM clock is an interesting thing. It is defined as "nanoseconds
> since the guest was created", but in practice it runs at two *different*
> rates — or three different rates, if you count implementation bugs.

LOL, nice.

> Definition C should simply be eliminated. Commit 451a707813ae ("KVM:
> x86/xen: improve accuracy of Xen timers") worked around it for the
> specific case of Xen timers, which are defined in terms of the KVM clock
> and suffered from a continually increasing error in timer expiry times.

IIUC, there should probably be a "But that's a problem for a different day" line
after this.  I.e. describing 'C' is purely for context, and removing the
KVM_REQ_MASTERCLOCK_UPDATE request doesn't move the needle on eliminating this
flaw, correct?

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