linux-kernel - Re: [PATCH v2 1/3] KVM: x86: implement KVM_{GET|SET}_TSC

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Message-ID: <87lfe5i4yk.fsf@nanos.tec.linutronix.de>
Date:   Fri, 11 Dec 2020 01:03:47 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        kvm list <kvm@...r.kernel.org>,
        "H. Peter Anvin" <hpa@...or.com>, Jonathan Corbet <corbet@....net>,
        Jim Mattson <jmattson@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        "open list\:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        open list <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        "maintainer\:X86 ARCHITECTURE \(32-BIT AND 64-BIT\)" <x86@...nel.org>,
        Joerg Roedel <joro@...tes.org>, Borislav Petkov <bp@...en8.de>,
        Shuah Khan <shuah@...nel.org>,
        Andrew Jones <drjones@...hat.com>,
        Oliver Upton <oupton@...gle.com>,
        "open list\:DOCUMENTATION" <linux-doc@...r.kernel.org>
Subject: Re: [PATCH v2 1/3] KVM: x86: implement KVM_{GET|SET}_TSC_STATE

On Thu, Dec 10 2020 at 15:19, Andy Lutomirski wrote:
>> On Dec 10, 2020, at 2:28 PM, Thomas Gleixner <tglx@...utronix.de> wrote:
>> Can we please focus on real problems instead of making up new ones?
>> 
>> Correctness of time is a real problem despite the believe of virt folks
>> that it can be ignored or duct taped to death.
>> 
> I’m fine with this as long as it’s intentional. If we say “guest
> timekeeping across host suspend is correct because we notify the
> guest”, then we have a hole. But if we say “the host will try to
> notify the guest, and if the guest is out to lunch then the host
> reserves the right to suspend without waiting, and the guest should
> deal with this”, then okay.

Yes of course this would be intentional and documented behaviour, which
is an infinite improvement over the current situation.

Thanks,

        tglx