[PATCH v2 4/6] x86/irq: Process nmi sources in NMI handler

[Jacob Pan]

With NMI source reporting enabled, NMI handler can prioritize the
handling of sources reported explicitly. If the source is unknown, then
resume the existing processing flow. i.e. invoke all NMI handlers.

Signed-off-by: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>

---
v2:
   - Disable NMI source reporting once garbage data is given in FRED
return stack. (HPA)
---
 arch/x86/kernel/nmi.c | 49 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 49 insertions(+)

diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c
index 639a34e78bc9..2c391fd59c34 100644
--- a/arch/x86/kernel/nmi.c
+++ b/arch/x86/kernel/nmi.c
@@ -149,12 +149,61 @@ static inline int do_handle_nmi(struct nmiaction *a, struct pt_regs *regs, unsig
 	return thishandled;
 }
 
+static inline int nmi_handle_src(unsigned int type, struct pt_regs *regs)
+{
+	unsigned long source_bitmask;
+	struct nmiaction *a;
+	int handled = 0;
+	int vec = 1;
+
+	if (!cpu_feature_enabled(X86_FEATURE_NMI_SOURCE) || type != NMI_LOCAL)
+		return 0;
+
+	source_bitmask = fred_event_data(regs);
+	if (!source_bitmask) {
+		pr_warn_ratelimited("NMI without source information! Disable source reporting.\n");
+		setup_clear_cpu_cap(X86_FEATURE_NMI_SOURCE);
+		return 0;
+	}
+
+	/*
+	 * Per NMI source specification, there is no guarantee that a valid
+	 * NMI vector is always delivered, even when the source specified
+	 * one. It is software's responsibility to check all available NMI
+	 * sources when bit 0 is set in the NMI source bitmap. i.e. we have
+	 * to call every handler as if we have no NMI source.
+	 * On the other hand, if we do get non-zero vectors, we know exactly
+	 * what the sources are. So we only call the handlers with the bit set.
+	 */
+	if (source_bitmask & BIT(NMI_SOURCE_VEC_UNKNOWN)) {
+		pr_warn_ratelimited("NMI received with unknown source\n");
+		return 0;
+	}
+
+	rcu_read_lock();
+	/* Bit 0 is for unknown NMI sources, skip it. */
+	for_each_set_bit_from(vec, &source_bitmask, NR_NMI_SOURCE_VECTORS) {
+		a = rcu_dereference(nmiaction_src_table[vec]);
+		if (!a) {
+			pr_warn_ratelimited("NMI received %d no handler", vec);
+			continue;
+		}
+		handled += do_handle_nmi(a, regs, type);
+	}
+	rcu_read_unlock();
+	return handled;
+}
+
 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;
 
+	handled = nmi_handle_src(type, regs);
+	if (handled)
+		return handled;
+
 	rcu_read_lock();
 
 	/*
-- 
2.25.1