linux-kernel - Re: [PATCH] livepatch: add (un)patch hooks

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Message-ID: <ffc9a367-8cbd-9461-4e10-2a2a32637104@redhat.com>
Date:   Fri, 28 Jul 2017 14:08:33 -0400
From:   Joe Lawrence <joe.lawrence@...hat.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Petr Mladek <pmladek@...e.com>, live-patching@...r.kernel.org,
        linux-kernel@...r.kernel.org, Jessica Yu <jeyu@...nel.org>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Chris J Arges <chris.j.arges@...onical.com>
Subject: Re: [PATCH] livepatch: add (un)patch hooks

On 07/27/2017 05:36 PM, Josh Poimboeuf wrote:
> On Thu, Jul 27, 2017 at 04:43:58PM -0400, Joe Lawrence wrote:
>> On 07/20/2017 12:17 AM, Josh Poimboeuf wrote:
>>> - The post-patch and post-unpatch hooks will need to be run from either
>>>   klp_complete_transition() or klp_module_coming/going(), depending on
>>>   whether the to-be-patched module is already loaded or is being
>>>   loaded/unloaded.
>>
>> You're suggesting that post-(un)patch-hooks:
>>
>>   1 - Notify klp_objects when a KLP_(UN)PATCHED transition completes
> 
> Right. (From klp_complete_transition())

We should be careful to only call hooks for those klp_objects that were
actually (un)patched.  I don't think there is such state that makes it
all the way out to klp_complete_transition(), but since both the
completion and module_coming/going code both operate under the
klp_mutex, perhaps klp_is_object_loaded() is a sufficient check?

>> and for subsequently loaded klp_objects (ie modules):
>>
>>   2 - On load - notify it with current KLP_(UN)PATCHED state,
>>       Steady state - same as (1) above.
> 
> Right. (From klp_module_coming/going())
> 

At least this should be easier to implement since we know what the story
is for the klp_object in hand.

-- Joe