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Subject: Re: [PATCH 1/2] KVM: X86: TSCDEADLINE MSR emulation fastpath
To:     Wanpeng Li <kernellwp@gmail.com>
Cc:     LKML <linux-kernel@vger.kernel.org>, kvm <kvm@vger.kernel.org>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Haiwei Li <lihaiwei@tencent.com>
References: <1587468026-15753-1-git-send-email-wanpengli@tencent.com>
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 <CANRm+CxzROx=eawemmzh==2Mz-DxKSyYFSxHqLxUiGFFnWkAYw@mail.gmail.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <d87e0a4b-608a-451b-e3f0-968d46b6cc26@redhat.com>
Date:   Wed, 22 Apr 2020 10:38:39 +0200
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On 22/04/20 02:48, Wanpeng Li wrote:
> On Tue, 21 Apr 2020 at 19:37, Paolo Bonzini <pbonzini@redhat.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.

>> 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.

Paolo