linux-kernel - Re: [PATCH v3 07/18] nitro_enclaves: Init misc device providing the ioctl interface

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Date:   Tue, 9 Jun 2020 12:47:27 +0200
From:   Alexander Graf <graf@...zon.de>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Greg KH <gregkh@...uxfoundation.org>
CC:     Andra Paraschiv <andraprs@...zon.com>,
        <linux-kernel@...r.kernel.org>,
        Anthony Liguori <aliguori@...zon.com>,
        Colm MacCarthaigh <colmmacc@...zon.com>,
        Bjoern Doebel <doebel@...zon.de>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Frank van der Linden <fllinden@...zon.com>,
        "Martin Pohlack" <mpohlack@...zon.de>,
        Matt Wilson <msw@...zon.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Balbir Singh <sblbir@...zon.com>,
        Stefano Garzarella <sgarzare@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Stewart Smith <trawets@...zon.com>,
        Uwe Dannowski <uwed@...zon.de>, <kvm@...r.kernel.org>,
        <ne-devel-upstream@...zon.com>
Subject: Re: [PATCH v3 07/18] nitro_enclaves: Init misc device providing the
 ioctl interface



On 01.06.20 05:04, Benjamin Herrenschmidt wrote:
> 
> 
> On Thu, 2020-05-28 at 15:12 +0200, Greg KH wrote:
>> So at runtime, after all is booted and up and going, you just ripped
>> cores out from under someone's feet?  :)
>>
>> And the code really handles writing to that value while the module is
>> already loaded and up and running?  At a quick glance, it didn't seem
>> like it would handle that very well as it only is checked at ne_init()
>> time.
>>
>> Or am I missing something?
>>
>> Anyway, yes, if you can dynamically do this at runtime, that's great,
>> but it feels ackward to me to rely on one configuration thing as a
>> module parameter, and everything else through the ioctl interface.
>> Unification would seem to be a good thing, right?
> 
> I personally still prefer a sysfs file :) I really don't like module
> parameters as a way to do such things.

I think we're going in circles :).

A module parameter initialized with module_param_cb gives us a sysfs 
file that can also have a default parameter set through easily available 
tooling.

The ioctl has two downsides:

   1) It relies on an external application
   2) The permission check would be strictly limited to CAP_ADMIN, sysfs 
files can have different permissions

So I fail to see how a module parameter is *not* giving both of you and 
me what we want? Of course only if it implements the callback. It was 
missing that and apologize for that oversight.


Alex



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