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Frederic Weisbecker
aed5ed4772
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 <[email protected]> Signed-off-by: Frederic Weisbecker <[email protected]> Reviewed-by: Rik van Riel <[email protected]> Acked-by: Peter Zijlstra (Intel) <[email protected]> Cc: Borislav Petkov <[email protected]> Cc: Chris Metcalf <[email protected]> Cc: H. Peter Anvin <[email protected]> Cc: Martin Schwidefsky <[email protected]> Cc: Mike Galbraith <[email protected]> Cc: Oleg Nesterov <[email protected]> Cc: Paul E. McKenney <[email protected]> Cc: Rafael J . Wysocki <[email protected]> Cc: Thomas Gleixner <[email protected]> Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Ingo Molnar <[email protected]>
49 lines
1.3 KiB
C
49 lines
1.3 KiB
C
#ifndef _LINUX_CONTEXT_TRACKING_STATE_H
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#define _LINUX_CONTEXT_TRACKING_STATE_H
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#include <linux/percpu.h>
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#include <linux/static_key.h>
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struct context_tracking {
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/*
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* When active is false, probes are unset in order
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* to minimize overhead: TIF flags are cleared
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* and calls to user_enter/exit are ignored. This
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* may be further optimized using static keys.
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*/
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bool active;
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int recursion;
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enum ctx_state {
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CONTEXT_KERNEL = 0,
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CONTEXT_USER,
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CONTEXT_GUEST,
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} state;
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};
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#ifdef CONFIG_CONTEXT_TRACKING
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extern struct static_key context_tracking_enabled;
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DECLARE_PER_CPU(struct context_tracking, context_tracking);
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static inline bool context_tracking_is_enabled(void)
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{
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return static_key_false(&context_tracking_enabled);
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}
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static inline bool context_tracking_cpu_is_enabled(void)
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{
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return __this_cpu_read(context_tracking.active);
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}
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static inline bool context_tracking_in_user(void)
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{
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return __this_cpu_read(context_tracking.state) == CONTEXT_USER;
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}
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#else
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static inline bool context_tracking_in_user(void) { return false; }
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static inline bool context_tracking_active(void) { return false; }
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static inline bool context_tracking_is_enabled(void) { return false; }
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static inline bool context_tracking_cpu_is_enabled(void) { return false; }
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#endif /* CONFIG_CONTEXT_TRACKING */
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#endif
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