18 #include <linux/nmi.h>
31 #include <asm/nmi.h>
39 #include <trace/events/nmi.h>
80  * Prevent NMI reason port (0x61) being accessed simultaneously, can
81  * only be used in NMI handler.
117 		"INFO: NMI handler (%ps) took too long to run: %lld.%03d msecs\n",  in nmi_check_duration()
150 	/* return total number of NMI events handled */  in nmi_handle()
167 	 * internal NMI handler call chains (SERR and IO_CHECK).  in __register_nmi_handler()
196 		 * the name passed in to describe the nmi handler  in unregister_nmi_handler()
201 				"Trying to free NMI (%s) from NMI context!\n", n->name);  in unregister_nmi_handler()
223 	pr_emerg("NMI: PCI system error (SERR) for reason %02x on CPU %d.\n",  in pci_serr_error()
227 		nmi_panic(regs, "NMI: Not continuing");  in pci_serr_error()
247 	"NMI: IOCK error (debug interrupt?) for reason %02x on CPU %d.\n",  in io_check_error()
252 		nmi_panic(regs, "NMI IOCK error: Not continuing");  in io_check_error()
255 		 * If we end up here, it means we have received an NMI while  in io_check_error()
286 	 * if it caused the NMI)  in unknown_nmi_error()
296 	pr_emerg("Uhhuh. NMI received for unknown reason %02x on CPU %d.\n",  in unknown_nmi_error()
300 		nmi_panic(regs, "NMI: Not continuing");  in unknown_nmi_error()
316 	 * CPU-specific NMI must be processed before non-CPU-specific  in default_do_nmi()
317 	 * NMI, otherwise we may lose it, because the CPU-specific  in default_do_nmi()
318 	 * NMI can not be detected/processed on other CPUs.  in default_do_nmi()
323 	 * be two NMI or more than two NMIs (any thing over two is dropped  in default_do_nmi()
324 	 * due to NMI being edge-triggered).  If this is the second half  in default_do_nmi()
325 	 * of the back-to-back NMI, assume we dropped things and process  in default_do_nmi()
326 	 * more handlers.  Otherwise reset the 'swallow' NMI behaviour  in default_do_nmi()
341 		 * There are cases when a NMI handler handles multiple  in default_do_nmi()
342 		 * events in the current NMI.  One of these events may  in default_do_nmi()
343 		 * be queued for in the next NMI.  Because the event is  in default_do_nmi()
344 		 * already handled, the next NMI will result in an unknown  in default_do_nmi()
345 		 * NMI.  Instead lets flag this for a potential NMI to  in default_do_nmi()
354 	 * Non-CPU-specific NMI: NMI sources can be processed on any CPU.  in default_do_nmi()
375 		 * Reassert NMI in case it became active  in default_do_nmi()
387 	 * Only one NMI can be latched at a time.  To handle  in default_do_nmi()
388 	 * this we may process multiple nmi handlers at once to  in default_do_nmi()
389 	 * cover the case where an NMI is dropped.  The downside  in default_do_nmi()
390 	 * to this approach is we may process an NMI prematurely,  in default_do_nmi()
391 	 * while its real NMI is sitting latched.  This will cause  in default_do_nmi()
392 	 * an unknown NMI on the next run of the NMI processing.  in default_do_nmi()
397 	 * of a back-to-back NMI, so we flag that condition too.  in default_do_nmi()
400 	 * NMI previously and we swallow it.  Otherwise we reset  in default_do_nmi()
404 	 * a 'real' unknown NMI.  For example, while processing  in default_do_nmi()
405 	 * a perf NMI another perf NMI comes in along with a  in default_do_nmi()
406 	 * 'real' unknown NMI.  These two NMIs get combined into  in default_do_nmi()
407 	 * one (as described above).  When the next NMI gets  in default_do_nmi()
409 	 * no one will know that there was a 'real' unknown NMI sent  in default_do_nmi()
411 	 * perf NMI returns two events handled then the second  in default_do_nmi()
412 	 * NMI will get eaten by the logic below, again losing a  in default_do_nmi()
413 	 * 'real' unknown NMI.  But this is the best we can do  in default_do_nmi()
427  * its NMI context with the CPU when the breakpoint or page fault does an IRET.
430  * NMI processing.  On x86_64, the asm glue protects us from nested NMIs
431  * if the outer NMI came from kernel mode, but we can still nest if the
432  * outer NMI came from user mode.
440  * When no NMI is in progress, it is in the "not running" state.
441  * When an NMI comes in, it goes into the "executing" state.
442  * Normally, if another NMI is triggered, it does not interrupt
443  * the running NMI and the HW will simply latch it so that when
444  * the first NMI finishes, it will restart the second NMI.
446  *  when one is running, are ignored. Only one NMI is restarted.)
448  * If an NMI executes an iret, another NMI can preempt it. We do not
449  * want to allow this new NMI to run, but we want to execute it when the
451  * the first NMI will perform a dec_return, if the result is zero
452  * (NOT_RUNNING), then it will simply exit the NMI handler. If not, the
455  * rerun the NMI handler again, and restart the 'latched' NMI.
462  * In case the NMI takes a page fault, we need to save off the CR2
463  * because the NMI could have preempted another page fault and corrupt
466  * CR2 must be done before converting the nmi state back to NOT_RUNNING.
467  * Otherwise, there would be a race of another nested NMI coming in
550 /* reset the back-to-back NMI logic */