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Message-ID: <20250513203803.2636561-5-sohil.mehta@intel.com>
Date: Tue, 13 May 2025 13:37:58 -0700
From: Sohil Mehta <sohil.mehta@...el.com>
To: x86@...nel.org,
linux-kernel@...r.kernel.org
Cc: Xin Li <xin@...or.com>,
"H . Peter Anvin" <hpa@...or.com>,
Andy Lutomirski <luto@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Peter Zijlstra <peterz@...radead.org>,
Sean Christopherson <seanjc@...gle.com>,
Adrian Hunter <adrian.hunter@...el.com>,
Kan Liang <kan.liang@...ux.intel.com>,
Tony Luck <tony.luck@...el.com>,
Zhang Rui <rui.zhang@...el.com>,
Steven Rostedt <rostedt@...dmis.org>,
Sohil Mehta <sohil.mehta@...el.com>,
Andrew Cooper <andrew.cooper3@...rix.com>,
"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
Jacob Pan <jacob.pan@...ux.microsoft.com>,
Andi Kleen <ak@...ux.intel.com>,
Kai Huang <kai.huang@...el.com>,
Sandipan Das <sandipan.das@....com>,
linux-perf-users@...r.kernel.org,
linux-edac@...r.kernel.org,
kvm@...r.kernel.org,
linux-pm@...r.kernel.org,
linux-trace-kernel@...r.kernel.org
Subject: [PATCH v6 4/9] x86/nmi: Assign and register NMI-source vectors
Prior to NMI-source support, the vector information was ignored by the
hardware while delivering NMIs. With NMI-source, the architecture
currently supports a 16-bit source bitmap to identify the source of the
NMI. Upon receiving an NMI, this bitmap is delivered as part of the FRED
event delivery mechanism to the kernel.
Assign a vector space of 0-15 that is specific to NMI-source and
independent of the IDT vector space of 0-255. Being a bitmap, the
NMI-source vectors do not have any inherent priority associated with
them. The order of executing the NMI handlers is up to the kernel.
Existing NMI handling already has a priority mechanism for the NMI
handlers, with CPU-specific (NMI_LOCAL) handlers executed first,
followed by platform NMI handlers and unknown NMI (NMI_UNKNOWN) handlers
being last. Within each of these NMI types, the handlers registered with
NMI_FLAG_FIRST are given priority.
NMI-source follows the same priority scheme to avoid unnecessary
complexity. Therefore, the NMI-source vectors are assigned arbitrarily,
except for vectors 0 and 2.
Vector 0 is set by the hardware whenever a source vector was not used
while generating an NMI or the originator could not be reliably
identified. Do not assign it to any handler.
Vector 2 is reserved for external NMIs corresponding to Local APIC -
LINT1. Some third-party chipsets may send NMI messages with a hardcoded
vector of 2, which would result in vector 2 being set in the NMI-source
bitmap. To avoid confusion, do not assign vector 2 to any handler.
NMI-source vectors are only assigned for NMI_LOCAL type handlers.
Platform NMI handlers have a single handler registered per type. They
don't need additional source information to differentiate among them.
Use the assigned vectors to register the respective NMI handlers. Warn
if the vector values are unexpected.
A couple of NMI handlers, such as the microcode rendezvous and the crash
reboot, do not use the typical NMI registration interface. Leave them
as-is for now.
Originally-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>
Signed-off-by: Sohil Mehta <sohil.mehta@...el.com>
---
v6: Store source vector unconditionally.
Add a warning for unexpected source vector values.
v5: Move the vector defines to nmi.h.
Combine vector allocation and registration into one patch.
Simplify NMI vector names.
Describe usage of vector 2 for external NMIs.
Get rid of vector priorities.
---
arch/x86/events/core.c | 2 +-
arch/x86/include/asm/nmi.h | 32 ++++++++++++++++++++++++++++++++
arch/x86/kernel/apic/hw_nmi.c | 2 +-
arch/x86/kernel/cpu/mce/inject.c | 2 +-
arch/x86/kernel/kgdb.c | 2 +-
arch/x86/kernel/nmi.c | 4 ++++
arch/x86/kernel/nmi_selftest.c | 2 +-
arch/x86/kernel/smp.c | 2 +-
8 files changed, 42 insertions(+), 6 deletions(-)
diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index b84b8be1f075..031e908f0d61 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -2115,7 +2115,7 @@ static int __init init_hw_perf_events(void)
x86_pmu.config_mask = X86_RAW_EVENT_MASK;
perf_events_lapic_init();
- register_nmi_handler(NMI_LOCAL, perf_event_nmi_handler, 0, "PMI", 0);
+ register_nmi_handler(NMI_LOCAL, perf_event_nmi_handler, 0, "PMI", NMIS_VECTOR_PMI);
unconstrained = (struct event_constraint)
__EVENT_CONSTRAINT(0, x86_pmu.cntr_mask64,
diff --git a/arch/x86/include/asm/nmi.h b/arch/x86/include/asm/nmi.h
index f0a577bf7bba..b9beb216f2d0 100644
--- a/arch/x86/include/asm/nmi.h
+++ b/arch/x86/include/asm/nmi.h
@@ -57,6 +57,38 @@ struct nmiaction {
u8 source_vector;
};
+/**
+ * NMI-source vectors are used to identify the origin of an NMI and to
+ * route the NMI directly to the appropriate handler.
+ *
+ * On CPUs that support NMI-source reporting with FRED, receiving an NMI
+ * with a valid vector sets the corresponding bit in the NMI-source
+ * bitmap. The bitmap is delivered as FRED event data on the stack.
+ * Multiple NMIs are coalesced in the NMI-source bitmap until the next
+ * NMI delivery.
+ *
+ * If an NMI is received without a vector or beyond the defined range,
+ * the CPU sets bit 0 of the NMI-source bitmap.
+ *
+ * Vector 2 is reserved for external NMIs related to the Local APIC -
+ * LINT1. Some third-party chipsets may send NMI messages with a
+ * hardcoded vector of 2, which would result in bit 2 being set in the
+ * NMI-source bitmap.
+ *
+ * The vectors are in no particular priority order. Add new vector
+ * assignments sequentially in the list below.
+ */
+#define NMIS_VECTOR_NONE 0 /* Reserved - Set for all unidentified sources */
+#define NMIS_VECTOR_TEST 1 /* NMI selftest */
+#define NMIS_VECTOR_EXTERNAL 2 /* Reserved - Match External NMI vector 2 */
+#define NMIS_VECTOR_SMP_STOP 3 /* Panic stop CPU */
+#define NMIS_VECTOR_BT 4 /* CPU backtrace */
+#define NMIS_VECTOR_KGDB 5 /* Kernel debugger */
+#define NMIS_VECTOR_MCE 6 /* MCE injection */
+#define NMIS_VECTOR_PMI 7 /* PerfMon counters */
+
+#define NMIS_VECTORS_MAX 16 /* Maximum number of NMI-source vectors */
+
/**
* register_nmi_handler - Register a handler for a specific NMI type
* @t: NMI type (e.g. NMI_LOCAL)
diff --git a/arch/x86/kernel/apic/hw_nmi.c b/arch/x86/kernel/apic/hw_nmi.c
index 612b77660d05..4e04f13d2de9 100644
--- a/arch/x86/kernel/apic/hw_nmi.c
+++ b/arch/x86/kernel/apic/hw_nmi.c
@@ -53,7 +53,7 @@ NOKPROBE_SYMBOL(nmi_cpu_backtrace_handler);
static int __init register_nmi_cpu_backtrace_handler(void)
{
- register_nmi_handler(NMI_LOCAL, nmi_cpu_backtrace_handler, 0, "arch_bt", 0);
+ register_nmi_handler(NMI_LOCAL, nmi_cpu_backtrace_handler, 0, "arch_bt", NMIS_VECTOR_BT);
return 0;
}
early_initcall(register_nmi_cpu_backtrace_handler);
diff --git a/arch/x86/kernel/cpu/mce/inject.c b/arch/x86/kernel/cpu/mce/inject.c
index 17804ba0b02f..a3c753dfce91 100644
--- a/arch/x86/kernel/cpu/mce/inject.c
+++ b/arch/x86/kernel/cpu/mce/inject.c
@@ -774,7 +774,7 @@ static int __init inject_init(void)
debugfs_init();
- register_nmi_handler(NMI_LOCAL, mce_raise_notify, 0, "mce_notify", 0);
+ register_nmi_handler(NMI_LOCAL, mce_raise_notify, 0, "mce_notify", NMIS_VECTOR_MCE);
mce_register_injector_chain(&inject_nb);
setup_inj_struct(&i_mce);
diff --git a/arch/x86/kernel/kgdb.c b/arch/x86/kernel/kgdb.c
index ab2d1b79b79e..9ca4b141da0c 100644
--- a/arch/x86/kernel/kgdb.c
+++ b/arch/x86/kernel/kgdb.c
@@ -602,7 +602,7 @@ int kgdb_arch_init(void)
if (retval)
goto out;
- retval = register_nmi_handler(NMI_LOCAL, kgdb_nmi_handler, 0, "kgdb", 0);
+ retval = register_nmi_handler(NMI_LOCAL, kgdb_nmi_handler, 0, "kgdb", NMIS_VECTOR_KGDB);
if (retval)
goto out1;
diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c
index be93ec7255bf..1a24e8df1bdf 100644
--- a/arch/x86/kernel/nmi.c
+++ b/arch/x86/kernel/nmi.c
@@ -182,6 +182,10 @@ int __register_nmi_handler(unsigned int type, struct nmiaction *action)
if (WARN_ON_ONCE(!action->handler || !list_empty(&action->list)))
return -EINVAL;
+ /* NMI-source reporting should only be used for NMI_LOCAL */
+ WARN_ON_ONCE(type != NMI_LOCAL && action->source_vector);
+ WARN_ON_ONCE(action->source_vector >= NMIS_VECTORS_MAX);
+
raw_spin_lock_irqsave(&desc->lock, flags);
/*
diff --git a/arch/x86/kernel/nmi_selftest.c b/arch/x86/kernel/nmi_selftest.c
index b203e4371816..5196023b31dc 100644
--- a/arch/x86/kernel/nmi_selftest.c
+++ b/arch/x86/kernel/nmi_selftest.c
@@ -63,7 +63,7 @@ static void __init test_nmi_ipi(struct cpumask *mask)
unsigned long timeout;
if (register_nmi_handler(NMI_LOCAL, test_nmi_ipi_callback, NMI_FLAG_FIRST,
- "nmi_selftest", 0, __initdata)) {
+ "nmi_selftest", NMIS_VECTOR_TEST, __initdata)) {
nmi_fail = FAILURE;
return;
}
diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c
index b80812aa06c3..5be1c0bdf901 100644
--- a/arch/x86/kernel/smp.c
+++ b/arch/x86/kernel/smp.c
@@ -143,7 +143,7 @@ DEFINE_IDTENTRY_SYSVEC(sysvec_reboot)
static int register_stop_handler(void)
{
return register_nmi_handler(NMI_LOCAL, smp_stop_nmi_callback, NMI_FLAG_FIRST, "smp_stop",
- 0);
+ NMIS_VECTOR_SMP_STOP);
}
static void native_stop_other_cpus(int wait)
--
2.43.0
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