linux-kernel - Re: [PATCH v2 3/4] KVM: async_pf: Force a nested vmexit if the injected #PF is async

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Date:   Fri, 16 Jun 2017 22:24:58 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Radim Krčmář <rkrcmar@...hat.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        kvm <kvm@...r.kernel.org>, Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>
Subject: Re: [PATCH v2 3/4] KVM: async_pf: Force a nested vmexit if the
 injected #PF is async_pf

2017-06-16 21:37 GMT+08:00 Radim Krčmář <rkrcmar@...hat.com>:
> 2017-06-14 19:26-0700, Wanpeng Li:
>> From: Wanpeng Li <wanpeng.li@...mail.com>
>>
>> Add an async_page_fault field to vcpu->arch.exception to identify an async
>> page fault, and constructs the expected vm-exit information fields. Force
>> a nested VM exit from nested_vmx_check_exception() if the injected #PF
>> is async page fault.
>>
>> Cc: Paolo Bonzini <pbonzini@...hat.com>
>> Cc: Radim Krčmář <rkrcmar@...hat.com>
>> Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
>> ---
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> @@ -452,7 +452,11 @@ EXPORT_SYMBOL_GPL(kvm_complete_insn_gp);
>>  void kvm_inject_page_fault(struct kvm_vcpu *vcpu, struct x86_exception *fault)
>>  {
>>       ++vcpu->stat.pf_guest;
>> -     vcpu->arch.cr2 = fault->address;
>> +     vcpu->arch.exception.async_page_fault = fault->async_page_fault;
>
> I think we need to act as if arch.exception.async_page_fault was not
> pending in kvm_vcpu_ioctl_x86_get_vcpu_events().  Otherwise, if we
> migrate with pending async_page_fault exception, we'd inject it as a
> normal #PF, which could confuse/kill the nested guest.
>
> And kvm_vcpu_ioctl_x86_set_vcpu_events() should clean the flag for
> sanity as well.

Do you mean we should add a field like async_page_fault to
kvm_vcpu_events::exception, then saves arch.exception.async_page_fault
to events->exception.async_page_fault through KVM_GET_VCPU_EVENTS and
restores events->exception.async_page_fault to
arch.exception.async_page_fault through KVM_SET_VCPU_EVENTS?

Regards,
Wanpeng Li