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 13:34:45 -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:
>> KVM provides a complete virtual system environment for guests, including
>> support for injecting interrupts modeled after the real
>> exception/interrupt
>> facilities present on the native platform (such as the IDT on x86).
>> Virtual interrupts can come from a variety of sources (emulated devices,
>> pass-through devices, etc) but all must be injected to the guest via
>> the KVM infrastructure.  This patch adds a new mechanism to inject a
>> specific
>> interrupt to a guest using a decoupled eventfd mechnanism:  Any legal
>> signal
>> on the irqfd (using eventfd semantics from either userspace or
>> kernel) will
>> translate into an injected interrupt in the guest at the next available
>> interrupt window.
>>
>>  
>> +struct kvm_irqfd {
>> +    __u32 gsi;
>> +    __u32 flags;
>> +};
>> +
>>   
>
> Please add some reserved space here.

Ack.  Any rule of thumb here?  How about a "__u8 pad[16]" ?

>
>> +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.

Good catch.  Will fix.

Thanks Avi,
-Greg



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