linux-kernel - [PATCH v2 12/45] arm64: mpam: Add helpers to change a task or cpu's MPAM PARTID/PMG values

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: <20251219181147.3404071-13-ben.horgan@arm.com>
Date: Fri, 19 Dec 2025 18:11:14 +0000
From: Ben Horgan <ben.horgan@....com>
To: ben.horgan@....com
Cc: amitsinght@...vell.com,
	baisheng.gao@...soc.com,
	baolin.wang@...ux.alibaba.com,
	carl@...amperecomputing.com,
	dave.martin@....com,
	david@...nel.org,
	dfustini@...libre.com,
	fenghuay@...dia.com,
	gshan@...hat.com,
	james.morse@....com,
	jonathan.cameron@...wei.com,
	kobak@...dia.com,
	lcherian@...vell.com,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	peternewman@...gle.com,
	punit.agrawal@....qualcomm.com,
	quic_jiles@...cinc.com,
	reinette.chatre@...el.com,
	rohit.mathew@....com,
	scott@...amperecomputing.com,
	sdonthineni@...dia.com,
	tan.shaopeng@...itsu.com,
	xhao@...ux.alibaba.com,
	catalin.marinas@....com,
	will@...nel.org,
	corbet@....net,
	maz@...nel.org,
	oupton@...nel.org,
	joey.gouly@....com,
	suzuki.poulose@....com,
	kvmarm@...ts.linux.dev,
	Dave Martin <Dave.Martin@....com>
Subject: [PATCH v2 12/45] arm64: mpam: Add helpers to change a task or cpu's MPAM PARTID/PMG values

From: James Morse <james.morse@....com>

Care must be taken when modifying the PARTID and PMG of a task in any
per-task structure as writing these values may race with the task being
scheduled in, and reading the modified values.

Add helpers to set the task properties, and the CPU default value.  These
use WRITE_ONCE() that pairs with the READ_ONCE() in mpam_get_regval() to
avoid causing torn values.

CC: Dave Martin <Dave.Martin@....com>
Signed-off-by: James Morse <james.morse@....com>
Signed-off-by: Ben Horgan <ben.horgan@....com>
---
Changes since rfc:
Keep comment attached to mpam_get_regval()
Add internal helper, __mpam_regval() (Jonathan)
---
 arch/arm64/include/asm/mpam.h | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/arch/arm64/include/asm/mpam.h b/arch/arm64/include/asm/mpam.h
index c4cb015e8d8f..a7fd0656bf90 100644
--- a/arch/arm64/include/asm/mpam.h
+++ b/arch/arm64/include/asm/mpam.h
@@ -4,6 +4,7 @@
 #ifndef __ASM__MPAM_H
 #define __ASM__MPAM_H
 
+#include <linux/bitfield.h>
 #include <linux/jump_label.h>
 #include <linux/percpu.h>
 #include <linux/sched.h>
@@ -22,6 +23,22 @@ DECLARE_PER_CPU(u64, arm64_mpam_current);
  */
 extern u64 arm64_mpam_global_default;
 
+static inline u64 __mpam_regval(u16 partid_d, u16 partid_i, u8 pmg_d, u8 pmg_i)
+{
+	return FIELD_PREP(MPAM0_EL1_PARTID_D, partid_d) |
+		FIELD_PREP(MPAM0_EL1_PARTID_I, partid_i) |
+		FIELD_PREP(MPAM0_EL1_PMG_D, pmg_d) |
+		FIELD_PREP(MPAM0_EL1_PMG_I, pmg_i);
+}
+
+static inline void mpam_set_cpu_defaults(int cpu, u16 partid_d, u16 partid_i,
+					 u8 pmg_d, u8 pmg_i)
+{
+	u64 default_val = __mpam_regval(partid_d, partid_i, pmg_d, pmg_i);
+
+	WRITE_ONCE(per_cpu(arm64_mpam_default, cpu), default_val);
+}
+
 /*
  * The resctrl filesystem writes to the partid/pmg values for threads and CPUs,
  * which may race with reads in mpam_thread_switch(). Ensure only one of the old
@@ -45,6 +62,17 @@ static inline u64 mpam_get_regval(struct task_struct *tsk)
 #endif
 }
 
+static inline void mpam_set_task_partid_pmg(struct task_struct *tsk,
+					    u16 partid_d, u16 partid_i,
+					    u8 pmg_d, u8 pmg_i)
+{
+#ifdef CONFIG_ARM64_MPAM
+	u64 regval = __mpam_regval(partid_d, partid_i, pmg_d, pmg_i);
+
+	WRITE_ONCE(task_thread_info(tsk)->mpam_partid_pmg, regval);
+#endif
+}
+
 static inline void mpam_thread_switch(struct task_struct *tsk)
 {
 	u64 oldregval;
-- 
2.43.0