linux-kernel - Re: [PATCH RFC 1/1] KVM: x86: add param to update master clock periodically

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Date:   Wed, 04 Oct 2023 09:06:14 +0100
From:   David Woodhouse <dwmw2@...radead.org>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Dongli Zhang <dongli.zhang@...cle.com>,
        Joe Jin <joe.jin@...cle.com>, x86@...nel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        pbonzini@...hat.com, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, dave.hansen@...ux.intel.com
Subject: Re: [PATCH RFC 1/1] KVM: x86: add param to update master clock
 periodically

On Tue, 2023-10-03 at 17:07 -0700, Sean Christopherson wrote:
> 
> The issue is that the timekeeping code doesn't provide a notification mechanism
> to *just* get updates for things like suspend/reume.  We could maybe do something
> in KVM like unregister the notifier if the TSC is constant, and manually refresh
> on suspend/resume.  But that's pretty gross too, and I'd definitely be concerned
> that we missed something.

Or *in* the existing notifier, just do the maths (correctly!) and don't
update KVM's raw_clock data if the only thing that's really changed is
the passage of time?

On the whole, it's better if your other patch works to avoid the drift
in the first place. I'll test it...

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