lists.openwall.net   lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  linux-cve-announce  PHC 
Open Source and information security mailing list archives
 
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20251013155205.2004838-3-lyude@redhat.com>
Date: Mon, 13 Oct 2025 11:48:04 -0400
From: Lyude Paul <lyude@...hat.com>
To: rust-for-linux@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Boqun Feng <boqun.feng@...il.com>,
	linux-kernel@...r.kernel.org,
	Daniel Almeida <daniel.almeida@...labora.com>
Cc: Joel Fernandes <joelagnelf@...dia.com>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>,
	Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>
Subject: [PATCH v13 02/17] preempt: Reduce NMI_MASK to single bit and restore HARDIRQ_BITS

From: Joel Fernandes <joelagnelf@...dia.com>

Now that NMI nesting is tracked in a separate per-CPU variable
(nmi_nesting), we no longer need multiple bits in preempt_count
for NMI tracking. Reduce NMI_BITS from 3 to 1, using it only to
detect if we're in an NMI.

Signed-off-by: Joel Fernandes <joelaf@...gle.com>
Signed-off-by: Lyude Paul <lyude@...hat.com>
---
 include/linux/preempt.h | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/include/linux/preempt.h b/include/linux/preempt.h
index 102202185d7a2..9580b972e1545 100644
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -17,6 +17,7 @@
  *
  * - bits 0-7 are the preemption count (max preemption depth: 256)
  * - bits 8-15 are the softirq count (max # of softirqs: 256)
+ * - bit 28 is the NMI flag (no nesting count, tracked separately)
  *
  * The hardirq count could in theory be the same as the number of
  * interrupts in the system, but we run all interrupt handlers with
@@ -24,16 +25,19 @@
  * there are a few palaeontologic drivers which reenable interrupts in
  * the handler, so we need more than one bit here.
  *
+ * NMI nesting depth is tracked in a separate per-CPU variable
+ * (nmi_nesting) to save bits in preempt_count.
+ *
  *         PREEMPT_MASK:	0x000000ff
  *         SOFTIRQ_MASK:	0x0000ff00
  *         HARDIRQ_MASK:	0x000f0000
- *             NMI_MASK:	0x00f00000
+ *             NMI_MASK:	0x10000000
  * PREEMPT_NEED_RESCHED:	0x80000000
  */
 #define PREEMPT_BITS	8
 #define SOFTIRQ_BITS	8
 #define HARDIRQ_BITS	4
-#define NMI_BITS	4
+#define NMI_BITS	1
 
 #define PREEMPT_SHIFT	0
 #define SOFTIRQ_SHIFT	(PREEMPT_SHIFT + PREEMPT_BITS)
-- 
2.51.0


Powered by blists - more mailing lists

Powered by Openwall GNU/*/Linux Powered by OpenVZ