linux-kernel - Re: [RFC PATCH v1.9 14/14] livepatch: update task universe when exiting kernel

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Date:	Thu, 14 Apr 2016 10:47:04 +0200 (CEST)
From:	Miroslav Benes <mbenes@...e.cz>
To:	Josh Poimboeuf <jpoimboe@...hat.com>
cc:	Jiri Kosina <jikos@...nel.org>, Jessica Yu <jeyu@...hat.com>,
	linux-kernel@...r.kernel.org, live-patching@...r.kernel.org,
	Vojtech Pavlik <vojtech@...e.com>
Subject: Re: [RFC PATCH v1.9 14/14] livepatch: update task universe when
 exiting kernel

On Fri, 25 Mar 2016, Josh Poimboeuf wrote:

> Update a tasks's universe when returning from a system call or user
> space interrupt, or after handling a signal.
> 
> This greatly increases the chances of a patch operation succeeding.  If
> a task is I/O bound, it can switch universes when returning from a
> system call.  If a task is CPU bound, it can switch universes when
> returning from an interrupt.  If a task is sleeping on a to-be-patched
> function, the user can send SIGSTOP and SIGCONT to force it to switch.
> 
> Since the idle "swapper" tasks don't ever exit the kernel, they're
> updated from within the idle loop.

Well, I am still not familiarized enough with Andy's recent rework of 
entry stuff, but I think all of this is correct. Maybe I would add 
a note to the changelog, that since TIF_KLP_NEED_UPDATE is defined 14th 
bit it is also automatically included in _TIF_ALLWORK_MASKS. 

> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
> ---
>  arch/x86/entry/common.c            |  6 +++++-
>  arch/x86/include/asm/thread_info.h |  2 ++
>  include/linux/livepatch.h          |  2 ++
>  kernel/livepatch/transition.c      | 37 +++++++++++++++++++++++++++++++++----
>  kernel/sched/idle.c                |  4 ++++
>  5 files changed, 46 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
> index e79d93d..94639dd 100644
> --- a/arch/x86/entry/common.c
> +++ b/arch/x86/entry/common.c
> @@ -21,6 +21,7 @@
>  #include <linux/context_tracking.h>
>  #include <linux/user-return-notifier.h>
>  #include <linux/uprobes.h>
> +#include <linux/livepatch.h>
>  
>  #include <asm/desc.h>
>  #include <asm/traps.h>
> @@ -202,7 +203,7 @@ long syscall_trace_enter(struct pt_regs *regs)
>  
>  #define EXIT_TO_USERMODE_LOOP_FLAGS				\
>  	(_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_UPROBE |	\
> -	 _TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY)
> +	 _TIF_NEED_RESCHED | _TIF_USER_RETURN_NOTIFY | _TIF_KLP_NEED_UPDATE)
>  
>  static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags)
>  {
> @@ -236,6 +237,9 @@ static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags)
>  		if (cached_flags & _TIF_USER_RETURN_NOTIFY)
>  			fire_user_return_notifiers();
>  
> +		if (unlikely(cached_flags & _TIF_KLP_NEED_UPDATE))
> +			klp_update_task_universe(current);
> +

There is a comment at the beginning of this function which should be 
updated as well I think.

Miroslav