linux-kernel - Re: [PATCH 4/4] KVM: async_pf: Let host know whether the guest support delivery async

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Date:   Wed, 14 Jun 2017 09:01:36 +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 4/4] KVM: async_pf: Let host know whether the guest
 support delivery async_pf as #PF vmexit

2017-06-14 2:19 GMT+08:00 Radim Krčmář <rkrcmar@...hat.com>:
> 2017-06-12 23:08-0700, Wanpeng Li:
>> From: Wanpeng Li <wanpeng.li@...mail.com>
>>
>> Adds another flag bit (bit 2) to MSR_KVM_ASYNC_PF_EN. If bit 2 is 1, async
>> page faults are delivered to L1 as #PF vmexits; if bit 2 is 0, kvm_can_do_async_pf
>> returns 0 if in guest mode.
>>
>> Cc: Paolo Bonzini <pbonzini@...hat.com>
>> Cc: Radim Krčmář <rkrcmar@...hat.com>
>> Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
>> ---
>
> I think KVM (L1) should also do something like
>
>   diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>   index dd274db9bf77..c15a9f178e60 100644
>   --- a/arch/x86/kvm/vmx.c
>   +++ b/arch/x86/kvm/vmx.c
>   @@ -7991,7 +7991,7 @@ static bool nested_vmx_exit_handled(struct kvm_vcpu *vcpu)
>                 if (is_nmi(intr_info))
>                         return false;
>                 else if (is_page_fault(intr_info))
>   -                     return enable_ept;
>   +                     return !vmx->apf_reason && enable_ept;
>                 else if (is_no_device(intr_info) &&
>                          !(vmcs12->guest_cr0 & X86_CR0_TS))
>                         return false;
>
> so it doesn't pass the APF directed towards it (L1) into L2 if there is
> L3 at the moment.

Agreed. I will do this in v2.

Regards,
Wanpeng Li