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 15:37:02 +0200
From:   Radim Krčmář <rkrcmar@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>
Cc:     linux-kernel@...r.kernel.org, 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

2017-06-14 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.

Thanks.