linux-kernel - Re: [PATCH v4] KVM: x86/tsc: Don't sync user changes to TSC with KVM-initiated change

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Date:   Wed, 13 Sep 2023 10:31:24 +0200
From:   David Woodhouse <dwmw2@...radead.org>
To:     Sean Christopherson <seanjc@...gle.com>,
        Like Xu <like.xu.linux@...il.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Oliver Upton <oliver.upton@...ux.dev>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] KVM: x86/tsc: Don't sync user changes to TSC with
 KVM-initiated change

On Fri, 2023-08-11 at 15:59 -0700, Sean Christopherson wrote:
> On Tue, Aug 01, 2023, Like Xu wrote:
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 278dbd37dab2..eeaf4ad9174d 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -2713,7 +2713,7 @@ static void __kvm_synchronize_tsc(struct kvm_vcpu *vcpu, u64 offset, u64 tsc,
> >         kvm_track_tsc_matching(vcpu);
> >   }
> >   
> > -static void kvm_synchronize_tsc(struct kvm_vcpu *vcpu, u64 data)
> > +static void kvm_synchronize_tsc(struct kvm_vcpu *vcpu, u64 data, bool user_initiated)
> 
> Rather than pass two somewhat magic values for the KVM-internal call, what about
> making @data a pointer and passing NULL?

Why change that at all?

Userspace used to be able to force a sync by writing zero. You are
removing that from the ABI without any explanation about why; it
doesn't seem necessary for fixing the original issue.

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