linux-kernel - Re: [PATCH 1/2] kvm: fix spurious interrupt with irqfd

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Message-ID: <20100119142902.GA28465@redhat.com>
Date:	Tue, 19 Jan 2010 16:29:02 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Jan Kiszka <jan.kiszka@...mens.com>
Cc:	Davide Libenzi <davidel@...ilserver.org>,
	Avi Kivity <avi@...hat.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] kvm: fix spurious interrupt with irqfd

On Tue, Jan 19, 2010 at 03:23:25PM +0100, Jan Kiszka wrote:
> Michael S. Tsirkin wrote:
> >>>> I just wonder how broad
> >>>> the impact of a broken or non-existent eventfd subsystem for kvm-kmod
> >>>> is. Any thoughts welcome.
> >>> How do you handle kernels that don't export eventfd_ctx_fileget?
> >> Now that you mention it: not yet properly. So far we pass the file
> >> struct as pseudo eventfd_ctx around on < 2.6.31. But now that I peek
> >> into the struct in kvm_eventfd_ctx_remove_wait_queue, this should should
> >> crash. Guess I need to look up that module the same way as I acquire
> >> __wake_up_locked[_key].
> > 
> > This won't work that well: eventfd in upstream
> > sends us POLLHUP so we can close the structure,
> > in old kernels it doesn't so kernel will crash
> > when we try to reference the structure later.
> > 
> 
> OK, so any host kernel < 2.6.31 will never work for us. Mmh, then I
> could only close the gap 2.6.31..2.6.33. vhost will show up in 33...
> Will that version already be worth any eventfd wrapping?
> 
> Jan

I asked Avi to send a patch upstream into 2.6.32.X fixing spurious
interrupts there. 2.6.31-stable is closed unfortunately, so we won't be
able to support it.  Disable eventfd there?

> -- 
> Siemens AG, Corporate Technology, CT T DE IT 1
> Corporate Competence Center Embedded Linux
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