linux-kernel - Re: [RFC PATCH 0/10] Cleaning up the KVM clock mess

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Date: Fri, 19 Apr 2024 13:52:49 +0100
From: David Woodhouse <dwmw2@...radead.org>
To: kvm@...r.kernel.org
Cc: Paolo Bonzini <pbonzini@...hat.com>, Jonathan Corbet <corbet@....net>, 
 Sean Christopherson <seanjc@...gle.com>, Thomas Gleixner
 <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov
 <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
 "H. Peter Anvin" <hpa@...or.com>,  Paul Durrant <paul@....org>, Shuah Khan
 <shuah@...nel.org>, linux-doc@...r.kernel.org, 
 linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org, Oliver Upton
 <oliver.upton@...ux.dev>, Marcelo Tosatti <mtosatti@...hat.com>, 
 jalliste@...zon.co.uk, sveith@...zon.de, Dongli Zhang
 <dongli.zhang@...cle.com>
Subject: Re: [RFC PATCH 0/10] Cleaning up the KVM clock mess

On Thu, 2024-04-18 at 20:34 +0100, David Woodhouse wrote:
> 
>       KVM: x86: Remove periodic global clock updates
>       KVM: x86: Kill KVM_REQ_GLOBAL_CLOCK_UPDATE

Meh, I might have to put those back. They were originally introduced to
cope with NTP frequency skew which is no longer a problem, but we now
know there's a systemic skew even between the host CLOCK_MONOTONIC_RAW
and the KVM clock as calculated via the guest's TSC.

So at least when !ka->use_master_clock I think the forced resync does
need to happen.

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