linux-kernel - Re: [PATCH 3/4] KVM: i8254: remove unnecessary irqchip_in

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Message-ID: <55B9D14D.1040600@redhat.com>
Date:	Thu, 30 Jul 2015 09:25:01 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Steve Rutherford <srutherford@...gle.com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	mtosatti@...hat.com, rkrcmar@...hat.com
Subject: Re: [PATCH 3/4] KVM: i8254: remove unnecessary irqchip_in_kernel
 check



On 30/07/2015 06:36, Steve Rutherford wrote:
> On Wed, Jul 29, 2015 at 03:28:57PM +0200, Paolo Bonzini wrote:
>> > The PIT is only created if irqchip_in_kernel returns true, so the
>> > check is superfluous.
> I poked around. Looks to me like the existence of an IOAPIC is not
> checked on the creation of the in-kernel PIT.

You're right, and presumably it's also legal to create the PIT before
KVM_CREATE_IRQCHIP.

> Userspace might limit itself to
> that scenario (PIT implies IOAPIC in-kernel), but that isn't enforced at PIT
> creation.

I'll play with the "PIT without IOAPIC" scenario and see if something
breaks badly with this patch.  From reading the code it seems like it
should not introduce any problems (oopses or similar), but I'll set this
patch aside for now.

Paolo
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