On Mon, 15 Jun 2009, tip-bot for Peter Zijlstra wrote: > > __copy_from_user_inatomic() isn't NMI safe in that it can trigger > the page fault handler which is another trap and its return path > invokes IRET which will also close the NMI context. That's not the only problem. An even more fundamental problem is that the page fault handler is not re-entrant because of simple the value in %cr2. So regardless of any 'iret' issues, you *CANNOT* take a page fault in an NMI, because the NMI might happen while we're in the critical region of having taken another page fault, but before we've saved off the value of %cr2 in that old page fault. If the NMI handler causes a page fault, it will corrupt the %cr2 of the outer page fault. That's why the page fault is done with an interrupt gate, and why we have that conditional local_irq_enable() in it. So page faults are fundamentally only safe wrt normal interrupts, not NMI. Linus -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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