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From: Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>
Subject: Re: [PATCH v2] KVM: x86: Inject pending interrupt even if pending
 nmi exist
Date: Wed, 23 Mar 2016 18:21:59 +0100
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Cc: Yuki Shibuya <shibuya.yk@ncos.nec.co.jp>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	Jan Kiszka <jan.kiszka@siemens.com>,
	Nobuo Yoshida <yoshida.nb@ncos.nec.co.jp>
To: Paolo Bonzini <pbonzini@redhat.com>
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2016-03-23 14:18+0100, Paolo Bonzini:
> On 23/03/2016 06:08, Yuki Shibuya wrote:
>> +		/* If nmi pending > 0 and injectable interrupts exist,
>> +		 * nmi pending counter is cleared to prevent skipping
>> +		 * injectable pending interrupts.
>> +		 */
>> +		if (vcpu->arch.nmi_pending && kvm_cpu_has_injectable_intr(vcpu)
>> +					&& kvm_x86_ops->interrupt_allowed(vcpu))
>> +			vcpu->arch.nmi_pending = 0;
> 
> I am not sure I understand this.  Why is it safe to drop nmi_pending?

NMIs are latched (queue length 1) and therefore cannot be pending after
an injection.  I think we want to do it unconditionally.

> Can we instead do something like this in vcpu_enter_guest?

(We should, even if it doesn't fix the bug.  Maskable interrupts can be
 injected while NMIs are blocked.)

What the hell is 2.6.32 doing, though?