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Subject[PATCH 4/5] x86, NMI: Allow NMI reason io port (0x61) to be processed on any CPU
Date
From: Huang Ying <ying.huang@intel.com>

In original NMI handler, NMI reason io port (0x61) is only processed
on BSP. This makes it impossible to hot-remove BSP. To solve the
issue, a raw spinlock is used to make the port can be processed on any
CPU.

Signed-off-by: Huang Ying <ying.huang@intel.com>
Signed-off-by: Don Zickus <dzickus@redhat.com>
---
arch/x86/kernel/traps.c | 45 +++++++++++++++++++++++++--------------------
1 files changed, 25 insertions(+), 20 deletions(-)
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index d8acab3..accb2f4 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -83,6 +83,12 @@ EXPORT_SYMBOL_GPL(used_vectors);

static int ignore_nmis;

+/*
+ * Prevent NMI reason port (0x61) being accessed simultaneously, can
+ * only be used in NMI handler.
+ */
+static DEFINE_RAW_SPINLOCK(nmi_reason_lock);
+
static inline void conditional_sti(struct pt_regs *regs)
{
if (regs->flags & X86_EFLAGS_IF)
@@ -383,7 +389,6 @@ unknown_nmi_error(unsigned char reason, struct pt_regs *regs)
static notrace __kprobes void default_do_nmi(struct pt_regs *regs)
{
unsigned char reason = 0;
- int cpu;

/*
* CPU-specific NMI must be processed before non-CPU-specific
@@ -400,28 +405,28 @@ static notrace __kprobes void default_do_nmi(struct pt_regs *regs)
return;

/* Non-CPU-specific NMI: NMI sources can be processed on any CPU */
- cpu = smp_processor_id();
- /* Only the BSP gets external NMIs from the system. */
- if (!cpu) {
- reason = get_nmi_reason();
- if (reason & NMI_REASON_MASK) {
- if (notify_die(DIE_NMI, "nmi", regs, reason, 2, SIGINT)
- == NOTIFY_STOP)
- return;
- if (reason & NMI_REASON_SERR)
- pci_serr_error(reason, regs);
- else if (reason & NMI_REASON_IOCHK)
- io_check_error(reason, regs);
+ raw_spin_lock(&nmi_reason_lock);
+ reason = get_nmi_reason();
+ if (reason & NMI_REASON_MASK) {
+ if (notify_die(DIE_NMI, "nmi", regs, reason, 2, SIGINT)
+ == NOTIFY_STOP)
+ goto unlock_return;
+ if (reason & NMI_REASON_SERR)
+ pci_serr_error(reason, regs);
+ else if (reason & 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();
+ /*
+ * Reassert NMI in case it became active
+ * meanwhile as it's edge-triggered:
+ */
+ reassert_nmi();
#endif
- return;
- }
+unlock_return:
+ raw_spin_unlock(&nmi_reason_lock);
+ return;
}
+ raw_spin_unlock(&nmi_reason_lock);

if (notify_die(DIE_NMI, "nmi", regs, 0, 2, SIGINT) == NOTIFY_STOP)
return;
--
1.7.2.3


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