linux-kernel - Re: [PATCH 2/2] ppc: kvm: use anon_inode_getfd() with O

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Date:	Mon, 26 Aug 2013 10:23:12 +0200
From:	Yann Droneaud <ydroneaud@...eya.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	Alexander Graf <agraf@...e.de>, Gleb Natapov <gleb@...hat.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Alex Williamson <alex.williamson@...hat.com>,
	kvm-ppc@...r.kernel.org, kvm@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	Paolo Bonzini <paolo.bonzini@...il.com>
Subject: Re: [PATCH 2/2] ppc: kvm: use anon_inode_getfd() with O_CLOEXEC flag

Le 26.08.2013 09:39, Paolo Bonzini a écrit :
> Il 25/08/2013 17:04, Alexander Graf ha scritto:
>> On 24.08.2013, at 21:14, Yann Droneaud wrote:
>> 
>>> 
>>> This patch set O_CLOEXEC flag on all file descriptors created
>>> with anon_inode_getfd() to not leak file descriptors across exec().
>>> 
>>> Signed-off-by: Yann Droneaud <ydroneaud@...eya.com>
>>> Link: 
>>> http://lkml.kernel.org/r/cover.1377372576.git.ydroneaud@opteya.com
>> 
>> Reviewed-by: Alexander Graf <agraf@...e.de>
>> 
>> Would it make sense to simply inherit the O_CLOEXEC flag from the
>> parent kvm fd instead? That would give user space the power to keep
>> fds across exec() if it wants to.
> 
> Does it make sense to use non-O_CLOEXEC file descriptors with KVM at
> all?  Besides fork() not being supported by KVM, as described in
> Documentation/virtual/kvm/api.txt, the VMAs of the parent process go
> away as soon as you exec().  I'm not sure how you can use the inherited
> file descriptor in a sensible way after exec().
> 

Sounds a lot like InfiniBand subsystem behavor: IB file descriptors
are of no use accross exec() since memory mappings tied to those fds
won't be available in the new process:

https://lkml.org/lkml/2013/7/8/380
http://mid.gmane.org/f58540dc64fec1ac0e496dfcd3cc1af7@meuh.org

Regards.

-- 
Yann Droneaud
OPTEYA

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