nmi中断
<h2>概述</h2>
<h2>处理流程</h2>
<pre><code class="language-c">// file: arch/x86/kernel/nmi.c
dotraplinkage notrace void
do_nmi(struct pt_regs *regs, long error_code)
{
if (this_cpu_read(nmi_state) != NMI_NOT_RUNNING) {
this_cpu_write(nmi_state, NMI_LATCHED);
return;
}
this_cpu_write(nmi_state, NMI_EXECUTING);
this_cpu_write(nmi_cr2, read_cr2());
nmi_restart:
#ifdef CONFIG_X86_64
/*
* If we interrupted a breakpoint, it is possible that
* the nmi handler will have breakpoints too. We need to
* change the IDT such that breakpoints that happen here
* continue to use the NMI stack.
*/
if (unlikely(is_debug_stack(regs-&gt;sp))) {
debug_stack_set_zero();
this_cpu_write(update_debug_stack, 1);
}
#endif
nmi_enter();
inc_irq_stat(__nmi_count);
if (!ignore_nmis)
default_do_nmi(regs); // 继续
nmi_exit();
#ifdef CONFIG_X86_64
if (unlikely(this_cpu_read(update_debug_stack))) {
debug_stack_reset();
this_cpu_write(update_debug_stack, 0);
}
#endif
if (unlikely(this_cpu_read(nmi_cr2) != read_cr2()))
write_cr2(this_cpu_read(nmi_cr2));
if (this_cpu_dec_return(nmi_state))
goto nmi_restart;
if (user_mode(regs))
mds_user_clear_cpu_buffers();
}
NOKPROBE_SYMBOL(do_nmi);
static DEFINE_PER_CPU(bool, swallow_nmi);
static DEFINE_PER_CPU(unsigned long, last_nmi_rip);
static void default_do_nmi(struct pt_regs *regs)
{
unsigned char reason = 0;
int handled;
bool b2b = false;
/*
* CPU-specific NMI must be processed before non-CPU-specific
* NMI, otherwise we may lose it, because the CPU-specific
* NMI can not be detected/processed on other CPUs.
*/
/*
* Back-to-back NMIs are interesting because they can either
* be two NMI or more than two NMIs (any thing over two is dropped
* due to NMI being edge-triggered). If this is the second half
* of the back-to-back NMI, assume we dropped things and process
* more handlers. Otherwise reset the 'swallow' NMI behaviour
*/
if (regs-&gt;ip == __this_cpu_read(last_nmi_rip))
b2b = true;
else
__this_cpu_write(swallow_nmi, false);
__this_cpu_write(last_nmi_rip, regs-&gt;ip);
handled = nmi_handle(NMI_LOCAL, regs); // 继续
__this_cpu_add(nmi_stats.normal, handled);
if (handled) {
/*
* There are cases when a NMI handler handles multiple
* events in the current NMI. One of these events may
* be queued for in the next NMI. Because the event is
* already handled, the next NMI will result in an unknown
* NMI. Instead lets flag this for a potential NMI to
* swallow.
*/
if (handled &gt; 1)
__this_cpu_write(swallow_nmi, true);
return;
}
/*
* Non-CPU-specific NMI: NMI sources can be processed on any CPU.
*
* Another CPU may be processing panic routines while holding
* nmi_reason_lock. Check if the CPU issued the IPI for crash dumping,
* and if so, call its callback directly. If there is no CPU preparing
* crash dump, we simply loop here.
*/
while (!raw_spin_trylock(&amp;nmi_reason_lock)) {
run_crash_ipi_callback(regs);
cpu_relax();
}
reason = x86_platform.get_nmi_reason();
if (reason &amp; NMI_REASON_MASK) {
if (reason &amp; NMI_REASON_SERR)
pci_serr_error(reason, regs);
else if (reason &amp; NMI_REASON_IOCHK)
io_check_error(reason, regs);
#ifdef CONFIG_X86_32
/*
* Reassert NMI in case it became active
* meanwhile as it's edge-triggered:
*/
reassert_nmi();
#endif
__this_cpu_add(nmi_stats.external, 1);
raw_spin_unlock(&amp;nmi_reason_lock);
return;
}
raw_spin_unlock(&amp;nmi_reason_lock);
/*
* Only one NMI can be latched at a time. To handle
* this we may process multiple nmi handlers at once to
* cover the case where an NMI is dropped. The downside
* to this approach is we may process an NMI prematurely,
* while its real NMI is sitting latched. This will cause
* an unknown NMI on the next run of the NMI processing.
*
* We tried to flag that condition above, by setting the
* swallow_nmi flag when we process more than one event.
* This condition is also only present on the second half
* of a back-to-back NMI, so we flag that condition too.
*
* If both are true, we assume we already processed this
* NMI previously and we swallow it. Otherwise we reset
* the logic.
*
* There are scenarios where we may accidentally swallow
* a 'real' unknown NMI. For example, while processing
* a perf NMI another perf NMI comes in along with a
* 'real' unknown NMI. These two NMIs get combined into
* one (as descibed above). When the next NMI gets
* processed, it will be flagged by perf as handled, but
* noone will know that there was a 'real' unknown NMI sent
* also. As a result it gets swallowed. Or if the first
* perf NMI returns two events handled then the second
* NMI will get eaten by the logic below, again losing a
* 'real' unknown NMI. But this is the best we can do
* for now.
*/
if (b2b &amp;&amp; __this_cpu_read(swallow_nmi))
__this_cpu_add(nmi_stats.swallow, 1);
else
unknown_nmi_error(reason, regs);
}
NOKPROBE_SYMBOL(default_do_nmi);
static int nmi_handle(unsigned int type, struct pt_regs *regs)
{
struct nmi_desc *desc = nmi_to_desc(type);
struct nmiaction *a;
int handled=0;
rcu_read_lock();
/*
* NMIs are edge-triggered, which means if you have enough
* of them concurrently, you can lose some because only one
* can be latched at any given time. Walk the whole list
* to handle those situations.
*/
list_for_each_entry_rcu(a, &amp;desc-&gt;head, list) {
int thishandled;
u64 delta;
delta = sched_clock();
thishandled = a-&gt;handler(type, regs);
handled += thishandled;
delta = sched_clock() - delta;
trace_nmi_handler(a-&gt;handler, (int)delta, thishandled);
nmi_check_duration(a, delta);
}
rcu_read_unlock();
/* return total number of NMI events handled */
return handled;
}
NOKPROBE_SYMBOL(nmi_handle);
</code></pre>