linux-kernel - Re: [RFC PATCH v5 064/104] KVM: TDX: Implement TDX vcpu enter/exit path

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Date:   Wed, 23 Mar 2022 13:05:27 -0700
From:   Erdem Aktas <erdemaktas@...gle.com>
To:     Isaku Yamahata <isaku.yamahata@...il.com>
Cc:     "Yamahata, Isaku" <isaku.yamahata@...el.com>,
        "open list:KERNEL VIRTUAL MACHINE (KVM)" <kvm@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Connor Kuehl <ckuehl@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>
Subject: Re: [RFC PATCH v5 064/104] KVM: TDX: Implement TDX vcpu enter/exit path

On Wed, Mar 23, 2022 at 10:55 AM Isaku Yamahata
<isaku.yamahata@...il.com> wrote:
>
> On Tue, Mar 22, 2022 at 10:28:42AM -0700,
> Erdem Aktas <erdemaktas@...gle.com> wrote:
>
> > On Fri, Mar 4, 2022 at 11:50 AM <isaku.yamahata@...el.com> wrote:
> > > @@ -509,6 +512,37 @@ void tdx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
> > >         vcpu->kvm->vm_bugged = true;
> > >  }
> > >
> > > +u64 __tdx_vcpu_run(hpa_t tdvpr, void *regs, u32 regs_mask);
> > > +
> > > +static noinstr void tdx_vcpu_enter_exit(struct kvm_vcpu *vcpu,
> > > +                                       struct vcpu_tdx *tdx)
> > > +{
> > > +       guest_enter_irqoff();
> > > +       tdx->exit_reason.full = __tdx_vcpu_run(tdx->tdvpr.pa, vcpu->arch.regs, 0);
> > > +       guest_exit_irqoff();
> > > +}
> > > +
> > > +fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu)
> > > +{
> > > +       struct vcpu_tdx *tdx = to_tdx(vcpu);
> > > +
> > > +       if (unlikely(vcpu->kvm->vm_bugged)) {
> > > +               tdx->exit_reason.full = TDX_NON_RECOVERABLE_VCPU;
> > > +               return EXIT_FASTPATH_NONE;
> > > +       }
> > > +
> > > +       trace_kvm_entry(vcpu);
> > > +
> > > +       tdx_vcpu_enter_exit(vcpu, tdx);
> > > +
> > > +       vcpu->arch.regs_avail &= ~VMX_REGS_LAZY_LOAD_SET;
> > > +       trace_kvm_exit(vcpu, KVM_ISA_VMX);
> > > +
> > > +       if (tdx->exit_reason.error || tdx->exit_reason.non_recoverable)
> > > +               return EXIT_FASTPATH_NONE;
> >
> > Looks like the above if statement has no effect. Just checking if this
> > is intentional.
>
> I'm not sure if I get your point.  tdx->exit_reason is updated by the above
> tdx_cpu_enter_exit().  So it makes sense to check .error or .non_recoverable.
> --
> Isaku Yamahata <isaku.yamahata@...il.com>

What I mean is, if there is an error, it returns EXIT_FASTPATH_NONE
but if there is no error, it still returns EXIT_FASTPATH_NONE.

The code is like below, the if-statement might be there as a
placeholder to check errors but it has no impact on what is returned
from this function.

       if (tdx->exit_reason.error || tdx->exit_reason.non_recoverable)
               return EXIT_FASTPATH_NONE;
       return EXIT_FASTPATH_NONE;