On Thu, Apr 14, 2016 at 10:47:04AM +0200, Miroslav Benes wrote:
> 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.
To be honest, putting it in the range of _TIF_ALLWORK_MASK was an
accident. I think the comments in thread_info.h need to be improved a
bit to make that clearer.
> > 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.
Yeah, agreed.
--
Josh
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