linux-kernel - Re: [PATCH 1/2] KVM: X86: TSCDEADLINE MSR emulation fastpath

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Date:   Wed, 22 Apr 2020 16:46:12 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Haiwei Li <lihaiwei@...cent.com>
Subject: Re: [PATCH 1/2] KVM: X86: TSCDEADLINE MSR emulation fastpath

On Wed, 22 Apr 2020 at 16:38, Paolo Bonzini <pbonzini@...hat.com> wrote:
>
> On 22/04/20 02:48, Wanpeng Li wrote:
> > On Tue, 21 Apr 2020 at 19:37, Paolo Bonzini <pbonzini@...hat.com> wrote:
> >> On 21/04/20 13:20, Wanpeng Li wrote:
> >>> +     case MSR_IA32_TSCDEADLINE:
> >>> +             if (!kvm_x86_ops.event_needs_reinjection(vcpu)) {
> >>> +                     data = kvm_read_edx_eax(vcpu);
> >>> +                     if (!handle_fastpath_set_tscdeadline(vcpu, data))
> >>> +                             ret = EXIT_FASTPATH_CONT_RUN;
> >>> +             }
> >>>               break;
> >> Can you explain the event_needs_reinjection case?  Also, does this break
> > This is used to catch the case vmexit occurred while another event was
> > being delivered to guest software, I move the
> > vmx_exit_handlers_fastpath() call after vmx_complete_interrupts()
> > which will decode such event and make kvm_event_needs_reinjection
> > return true.
>
> This doesn't need a callback, kvm_event_needs_reinjection should be enough.
>
> You should also check other conditions such as
>
>         vcpu->mode == EXITING_GUEST_MODE || kvm_request_pending(vcpu)
>             || need_resched() || signal_pending(current)
>
> before doing CONT_RUN.

Agreed.

>
> >> AMD which does not implement the callback?
> > Now I add the tscdeadline msr emulation and vmx-preemption timer
> > fastpath pair for Intel platform.
>
> But this would cause a crash if you run on AMD.

Yes. :)

    Wanpeng