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

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Message-ID: <4B55C05D.9000509@siemens.com>
Date:	Tue, 19 Jan 2010 15:23:25 +0100
From:	Jan Kiszka <jan.kiszka@...mens.com>
To:	"Michael S. Tsirkin" <mst@...hat.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

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

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