linux-kernel - Re: [PATCH 4/4] add ksm kernel shared memory driver.

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Message-ID: <20090331142533.GR9137@random.random>
Date:	Tue, 31 Mar 2009 16:25:33 +0200
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Anthony Liguori <anthony@...emonkey.ws>
Cc:	Izik Eidus <ieidus@...hat.com>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, linux-mm@...ck.org, avi@...hat.com,
	chrisw@...hat.com, riel@...hat.com, jeremy@...p.org,
	mtosatti@...hat.com, hugh@...itas.com, corbet@....net,
	yaniv@...hat.com, dmonakhov@...nvz.org
Subject: Re: [PATCH 4/4] add ksm kernel shared memory driver.

On Tue, Mar 31, 2009 at 08:31:31AM -0500, Anthony Liguori wrote:
> You could drop KSM_START_STOP_KTHREAD and KSM_GET_INFO_KTHREAD altogether, 
> and introduce a sysfs hierarchy:
>
> /sysfs/<some/path>/ksm/{enable,pages_to_scan,sleep_time}

Introducing a sysfs hierarchy sounds a bit of overkill.

> the ability to disable KSM.  That seems like a security concern to me since 
> registering a memory region ought to be an unprivileged action whereas 
> enabling/disabling KSM ought to be a privileged action.

sysfs files would then only be writeable by admin, so if we want to
allow only admin to start/stop/tune ksm it'd be enough to plug an
admin capability check in the ioctl to provide equivalent permissions.

I could imagine converting the enable/pages_to_scan/sleep_time to
module params and tweaking them through /sys/module/ksm/parameters,
but for "enable" to work that way, we'd need to intercept the write so
we can at least weakup the kksmd daemon, which doesn't seem possible
with /sys/module/ksm/parameters, so in the end if we stick to the
ioctl for registering regions, it seems simpler to use it for
start/stop/tune too.
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