linux-kernel - Re: [PATCH] KVM: x86: Check for nested events if there is an injectable interrupt

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Message-ID: <53BBA523.4080006@redhat.com>
Date:	Tue, 08 Jul 2014 10:00:35 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Jan Kiszka <jan.kiszka@...mens.com>, Bandan Das <bsd@...hat.com>,
	kvm@...r.kernel.org
CC:	linux-kernel@...r.kernel.org,
	Wanpeng Li <wanpeng.li@...ux.intel.com>,
	Gleb Natapov <gleb@...nel.org>
Subject: Re: [PATCH] KVM: x86: Check for nested events if there is an injectable
 interrupt

Il 08/07/2014 08:56, Jan Kiszka ha scritto:
> I don't think arch.nmi_pending can flip asynchronously, only in the
> context of the VCPU thread - in contrast to pending IRQ states.

Right, only nmi_queued is changed from other threads.  /me should really 
look at the code instead of going from memory.

>> Jan, what do you think?  Can you run Jailhouse through this patch?
>
> Jailhouse seems fine with it, and it resolves the lockup of nested KVM
> here as well.

Thinking more about it, I think this is the right fix.  Not setting 
KVM_REQ_EVENT in some cases can be an optimization, but it's not 
necessary.  Definitely there are other cases in which KVM_REQ_EVENT is 
set even though no event is pending---most notably during emulation of 
invalid guest state.

Paolo
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