linux-toradex.git/kernel/context_tracking.c, branch v4.12-rc1

context_tracking: Switch to new static_branch API

2015-11-24T08:56:43+00:00

This is much less error-prone than the old code.

Signed-off-by: Andy Lutomirski 
Cc: Andy Lutomirski 
Cc: Borislav Petkov 
Cc: Brian Gerst 
Cc: Denys Vlasenko 
Cc: Frederic Weisbecker 
Cc: H. Peter Anvin 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Link: http://lkml.kernel.org/r/812df7e64f120c5c7c08481f36a8caa9f53b2199.1447361906.git.luto@kernel.org
Signed-off-by: Ingo Molnar

context_tracking: avoid irq_save/irq_restore on guest entry and exit

2015-11-10T11:06:23+00:00

guest_enter and guest_exit must be called with interrupts disabled,
since they take the vtime_seqlock with write_seq{lock,unlock}.
Therefore, it is not necessary to check for exceptions, nor to
save/restore the IRQ state, when context tracking functions are
called by guest_enter and guest_exit.

Split the body of context_tracking_entry and context_tracking_exit
out to __-prefixed functions, and use them from KVM.

Rik van Riel has measured this to speed up a tight vmentry/vmexit
loop by about 2%.

Cc: Andy Lutomirski 
Cc: Frederic Weisbecker 
Cc: Paul McKenney 
Reviewed-by: Rik van Riel 
Tested-by: Rik van Riel 
Signed-off-by: Paolo Bonzini

context_tracking: remove duplicate enabled check

2015-11-10T11:06:22+00:00

All calls to context_tracking_enter and context_tracking_exit
are already checking context_tracking_is_enabled, except the
context_tracking_user_enter and context_tracking_user_exit
functions left in for the benefit of assembly calls.

Pull the check up to those functions, by making them simple
wrappers around the user_enter and user_exit inline functions.

Cc: Frederic Weisbecker 
Cc: Paul McKenney 
Reviewed-by: Rik van Riel 
Tested-by: Rik van Riel 
Acked-by: Andy Lutomirski 
Signed-off-by: Paolo Bonzini

context_tracking: Inherit TIF_NOHZ through forks instead of context switches

2015-05-07T10:02:51+00:00

TIF_NOHZ is used by context_tracking to force syscall slow-path
on every task in order to track userspace roundtrips. As such,
it must be set on all running tasks.

It's currently explicitly inherited through context switches.
There is no need to do it in this fast-path though. The flag
could simply be set once for all on all tasks, whether they are
running or not.

Lets do this by setting the flag for the init task on early boot,
and let it propagate through fork inheritance.

While at it, mark context_tracking_cpu_set() as init code, we
only need it at early boot time.

Suggested-by: Oleg Nesterov 
Signed-off-by: Frederic Weisbecker 
Reviewed-by: Rik van Riel 
Cc: Borislav Petkov 
Cc: Chris Metcalf 
Cc: Dave Jones 
Cc: H. Peter Anvin 
Cc: Martin Schwidefsky 
Cc: Mike Galbraith 
Cc: Paul E . McKenney 
Cc: Paul E. McKenney 
Cc: Peter Zijlstra 
Cc: Rafael J . Wysocki 
Cc: Thomas Gleixner 
Link: http://lkml.kernel.org/r/1430928266-24888-3-git-send-email-fweisbec@gmail.com
Signed-off-by: Ingo Molnar

context_tracking: Protect against recursion

2015-05-07T10:02:50+00:00

Context tracking recursion can happen when an exception triggers
in the middle of a call to a context tracking probe.

This special case can be caused by vmalloc faults. If an access
to a memory area allocated by vmalloc happens in the middle of
context_tracking_enter(), we may run into an endless fault loop
because the exception in turn calls context_tracking_enter()
which faults on the same vmalloc'ed memory, triggering an
exception again, etc...

Some rare crashes have been reported so lets protect against
this with a recursion counter.

Reported-by: Dave Jones 
Signed-off-by: Frederic Weisbecker 
Reviewed-by: Rik van Riel 
Acked-by: Peter Zijlstra (Intel) 
Cc: Borislav Petkov 
Cc: Chris Metcalf 
Cc: H. Peter Anvin 
Cc: Martin Schwidefsky 
Cc: Mike Galbraith 
Cc: Oleg Nesterov 
Cc: Paul E. McKenney 
Cc: Rafael J . Wysocki 
Cc: Thomas Gleixner 
Link: http://lkml.kernel.org/r/1430928266-24888-2-git-send-email-fweisbec@gmail.com
Signed-off-by: Ingo Molnar

context_tracking: Export context_tracking_user_enter/exit

2015-03-09T14:43:00+00:00

Export context_tracking_user_enter/exit so it can be used by KVM.

Reviewed-by: Paul E. McKenney 
Signed-off-by: Rik van Riel 
Cc: Paul E. McKenney 
Cc: Andy Lutomirski 
Cc: Will deacon 
Cc: Marcelo Tosatti 
Cc: Christian Borntraeger 
Cc: Luiz Capitulino 
Cc: Paolo Bonzini 
Signed-off-by: Frederic Weisbecker

context_tracking: Run vtime_user_enter/exit only when state == CONTEXT_USER

2015-03-09T14:42:57+00:00

Only run vtime_user_enter, vtime_user_exit, and the user enter & exit
trace points when we are entering or exiting user state, respectively.

The KVM code in guest_enter and guest_exit already take care of calling
vtime_guest_enter and vtime_guest_exit, respectively.

The RCU code only distinguishes between "idle" and "not idle or kernel".
There should be no need to add an additional (unused) state there.

Reviewed-by: Paul E. McKenney 
Signed-off-by: Rik van Riel 
Cc: Paul E. McKenney 
Cc: Andy Lutomirski 
Cc: Will deacon 
Cc: Marcelo Tosatti 
Cc: Christian Borntraeger 
Cc: Luiz Capitulino 
Cc: Paolo Bonzini 
Signed-off-by: Frederic Weisbecker

context_tracking: Generalize context tracking APIs to support user and guest

2015-03-09T14:42:52+00:00

Generalize the context tracking APIs to support various nature of
contexts. This is performed by splitting out the mechanism from
context_tracking_user_enter and context_tracking_user_exit into
context_tracking_enter and context_tracking_exit.

The nature of the context we track is now detailed in a ctx_state
parameter pushed to these APIs, allowing the same functions to not just
track kernel <> user space switching, but also kernel <> guest transitions.

But leave the old functions in order to avoid breaking ARM, which calls
these functions from assembler code, and cannot easily use C enum
parameters.

Reviewed-by: Paul E. McKenney 
Signed-off-by: Rik van Riel 
Cc: Paul E. McKenney 
Cc: Andy Lutomirski 
Cc: Will deacon 
Cc: Marcelo Tosatti 
Cc: Christian Borntraeger 
Cc: Luiz Capitulino 
Cc: Paolo Bonzini 
Signed-off-by: Frederic Weisbecker

context_tracking: Rename context symbols to prepare for transition state

2015-03-09T14:42:50+00:00

Current context tracking symbols are designed to express living state.
As such they are prefixed with "IN_": IN_USER, IN_KERNEL.

Now we are going to use these symbols to also express state transitions
such as context_tracking_enter(IN_USER) or context_tracking_exit(IN_USER).
But while the "IN_" prefix works well to express entering a context, it's
confusing to depict a context exit: context_tracking_exit(IN_USER)
could mean two things:
	1) We are exiting the current context to enter user context.
	2) We are exiting the user context
We want 2) but the reviewer may be confused and understand 1)

So lets disambiguate these symbols and rename them to CONTEXT_USER and
CONTEXT_KERNEL.

Acked-by: Rik van Riel 
Cc: Paul E. McKenney 
Cc: Andy Lutomirski 
Cc: Will deacon 
Cc: Marcelo Tosatti 
Cc: Christian Borntraeger 
Cc: Luiz Capitulino 
Cc: Paolo Bonzini 
Signed-off-by: Frederic Weisbecker

sched: stop the unbound recursion in preempt_schedule_context()

2014-10-28T09:46:05+00:00

preempt_schedule_context() does preempt_enable_notrace() at the end
and this can call the same function again; exception_exit() is heavy
and it is quite possible that need-resched is true again.

1. Change this code to dec preempt_count() and check need_resched()
   by hand.

2. As Linus suggested, we can use the PREEMPT_ACTIVE bit and avoid
   the enable/disable dance around __schedule(). But in this case
   we need to move into sched/core.c.

3. Cosmetic, but x86 forgets to declare this function. This doesn't
   really matter because it is only called by asm helpers, still it
   make sense to add the declaration into asm/preempt.h to match
   preempt_schedule().

Reported-by: Sasha Levin 
Signed-off-by: Oleg Nesterov 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Alexander Graf 
Cc: Andrew Morton 
Cc: Christoph Lameter 
Cc: Linus Torvalds 
Cc: Masami Hiramatsu 
Cc: Steven Rostedt 
Cc: Peter Anvin 
Cc: Andy Lutomirski 
Cc: Denys Vlasenko 
Cc: Chuck Ebbert 
Cc: Frederic Weisbecker 
Link: http://lkml.kernel.org/r/20141005202322.GB27962@redhat.com
Signed-off-by: Ingo Molnar