linux-kernel - Re: [PATCH v2] KVM: nVMX: Fix losing NMI blocking state

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Date:   Tue, 25 Jul 2017 15:00:20 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        kvm <kvm@...r.kernel.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>
Subject: Re: [PATCH v2] KVM: nVMX: Fix losing NMI blocking state

On 25/07/2017 13:36, Wanpeng Li wrote:
>>  - during VMRESUME emulation, prepare_vmcs02 sets bit 3 in the
>>    interruptibility-state field of vmcs02, but nmi_known_unmasked is
>>    still true.
>>  - on the next L2 exit to L0, nmi_known_unmasked is true so
>>    vmx_recover_nmi_blocking does not do anything.
>> 
>> Can you explain instead what happens if your v1 patch is applied (on top of mine),
>> and why it fixes the bug.
>
> We will set the expected guest interruptibility-state field before the
> final step: L0 fixes the shadow page table (NGVA -> HPA), then L0
> resumes the guest w/ the expected guest interruptibility-state.

Aha, that makes sense indeed!  I was confused between the first page
fault (that is reflected to L1) and the second (that is fixed by L0).

Thanks!

Paolo