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x86: Reset the debug_stack update counter 

When an NMI goes off and it sees that it preempted the debug stack,
to keep the debug stack safe, it changes the IDT to point to one that
does not modify the stack on breakpoint (to allow breakpoints in NMIs).

But the variable that gets set to know to undo it on exit never gets
cleared on exit. Thus every NMI will reset it on exit the first time
it is done even if it does not need to be reset.

[ Added H. Peter Anvin's suggestion to use this_cpu_read/write ]

Cc: <stable@vger.kernel.org> # v3.3
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt 2012-05-30 11:43:19 -04:00 committed by Steven Rostedt
parent 8a4d0a687a
commit c0525a6972
1 changed files with 4 additions and 2 deletions
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6
arch/x86/kernel/nmi.c
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@ -444,14 +444,16 @@ static inline void nmi_nesting_preprocess(struct pt_regs *regs)
*/
if (unlikely(is_debug_stack(regs->sp))) {
debug_stack_set_zero();
__get_cpu_var(update_debug_stack) = 1;
this_cpu_write(update_debug_stack, 1);
}
}
static inline void nmi_nesting_postprocess(void)
{
if (unlikely(__get_cpu_var(update_debug_stack)))
if (unlikely(this_cpu_read(update_debug_stack))) {
debug_stack_reset();
this_cpu_write(update_debug_stack, 0);
}
}
#endif