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@xxxxxxxxxx>
> ---
> 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
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