linux-kernel - [PATCH v4 5/5] arm64: make the per-task SCTLR2

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Message-Id: <20250821172408.2101870-6-yeoreum.yun@arm.com>
Date: Thu, 21 Aug 2025 18:24:08 +0100
From: Yeoreum Yun <yeoreum.yun@....com>
To: catalin.marinas@....com,
	will@...nel.org,
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Cc: linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org,
	kvmarm@...ts.linux.dev,
	Yeoreum Yun <yeoreum.yun@....com>
Subject: [PATCH v4 5/5] arm64: make the per-task SCTLR2_EL1

Some bits in SCTLR2_EL1 that control system behavior can be
configured on a per-task basis (e.g., fields related to FEAT_CPA2).
To support future use of these fields, SCTLR2_EL1 is maintained
per task.

On platforms without FEAT_SCTLR2 support, there is no functional
change and only minimal performance overhead.

Signed-off-by: Yeoreum Yun <yeoreum.yun@....com>
---
 arch/arm64/include/asm/processor.h | 3 +++
 arch/arm64/kernel/process.c        | 9 +++++++++
 2 files changed, 12 insertions(+)

diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
index 61d62bfd5a7b..e066116735c6 100644
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h
@@ -184,6 +184,7 @@ struct thread_struct {
 	u64			mte_ctrl;
 #endif
 	u64			sctlr_user;
+	u64			sctlr2_user;
 	u64			svcr;
 	u64			tpidr2_el0;
 	u64			por_el0;
@@ -258,6 +259,8 @@ static inline void task_set_sve_vl_onexec(struct task_struct *task,
 	(SCTLR_ELx_ENIA | SCTLR_ELx_ENIB | SCTLR_ELx_ENDA | SCTLR_ELx_ENDB |   \
 	 SCTLR_EL1_TCF0_MASK)
 
+#define SCTLR2_USER_MASK	(0)
+
 static inline void arch_thread_struct_whitelist(unsigned long *offset,
 						unsigned long *size)
 {
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 96482a1412c6..e54f192c0629 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -698,6 +698,11 @@ void update_sctlr_el1(u64 sctlr)
 	isb();
 }
 
+static void update_sctlr2_el1(u64 sctlr2)
+{
+	sysreg_clear_set_s(SYS_SCTLR2_EL1, SCTLR2_USER_MASK, sctlr2);
+}
+
 /*
  * Thread switching.
  */
@@ -737,6 +742,10 @@ struct task_struct *__switch_to(struct task_struct *prev,
 	if (prev->thread.sctlr_user != next->thread.sctlr_user)
 		update_sctlr_el1(next->thread.sctlr_user);
 
+	if (alternative_has_cap_unlikely(ARM64_HAS_SCTLR2) &&
+	    prev->thread.sctlr2_user != next->thread.sctlr2_user)
+		update_sctlr2_el1(next->thread.sctlr2_user);
+
 	/* the actual thread switch */
 	last = cpu_switch_to(prev, next);
 
-- 
LEVI:{C3F47F37-75D8-414A-A8BA-3980EC8A46D7}