linux-kernel - Re: [KVM PATCH v4 2/2] kvm: add support for irqfd via eventfd-notification interface

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Date:	Tue, 05 May 2009 13:56:42 -0400
From:	Gregory Haskins <ghaskins@...ell.com>
To:	Avi Kivity <avi@...hat.com>
CC:	kvm@...r.kernel.org, viro@...IV.linux.org.uk,
	linux-kernel@...r.kernel.org, davidel@...ilserver.org
Subject: Re: [KVM PATCH v4 2/2] kvm: add support for irqfd via	eventfd-notification
 interface

Avi Kivity wrote:
> Gregory Haskins wrote:
>
>> +int
>> +kvm_irqfd(struct kvm *kvm, int gsi, int flags)
>> +{
>> +    struct _irqfd *irqfd;
>> +    struct file *file = NULL;
>> +    int fd = -1;
>> +    int ret;
>> +
>> +    irqfd = kzalloc(sizeof(*irqfd), GFP_KERNEL);
>> +    if (!irqfd)
>> +        return -ENOMEM;
>> +
>> +    irqfd->kvm = kvm;
>>   
>
> You need to increase the refcount on struct kvm here.  Otherwise evil
> userspace will create an irqfd, close the vm and vcpu fds, and inject
> an interrupt.

I just reviewed the code in prep for v5, and now I remember why I didnt
take a reference:  I designed it the opposite direction:  the vm-fd owns
a reference to the irqfd, and will decouple the kvm context from the
eventfd on shutdown  (see kvm_irqfd_release()).   I still need to spin a
v5 regardless in order to add the padding as previously discussed.  But
let me know if you still see any holes in light of this alternate object
lifetime approach I am using.

-Greg

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