[PATCH 2/3] tso: aarch64: context-switch tso bit on thread switch

[Zayd Qumsieh]

Add support for context-switching the tso bit when the thread
switches. This allows per-thread setting of the tso bit, and prepares
future work to allow userspace to set the tso bit of their thread
at will.

Signed-off-by: Zayd Qumsieh <zayd_qumsieh at apple.com>
---
 arch/arm64/include/asm/processor.h | 4 ++++
 arch/arm64/include/asm/tso.h       | 1 +
 arch/arm64/kernel/process.c        | 9 +++++++++
 arch/arm64/kernel/tso.c            | 9 +++++++++
 4 files changed, 23 insertions(+)

diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
index f77371232d8c..a247bee24c73 100644
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h
@@ -4,6 +4,7 @@
  *
  * Copyright (C) 1995-1999 Russell King
  * Copyright (C) 2012 ARM Ltd.
+ * Copyright © 2024 Apple Inc. All rights reserved.
  */
 #ifndef __ASM_PROCESSOR_H
 #define __ASM_PROCESSOR_H
@@ -184,6 +185,9 @@ struct thread_struct {
 	u64			sctlr_user;
 	u64			svcr;
 	u64			tpidr2_el0;
+#ifdef CONFIG_ARM64_TSO
+	bool        tso;
+#endif
 };
 
 static inline unsigned int thread_get_vl(struct thread_struct *thread,
diff --git a/arch/arm64/include/asm/tso.h b/arch/arm64/include/asm/tso.h
index d9e1a7602c44..405e9a5efdf5 100644
--- a/arch/arm64/include/asm/tso.h
+++ b/arch/arm64/include/asm/tso.h
@@ -12,6 +12,7 @@
 #include <linux/types.h>
 
 int modify_tso_enable(bool tso_enable);
+void tso_thread_switch(struct task_struct *next);
 
 #endif /* CONFIG_ARM64_TSO */
 #endif /* __ASM_TSO_H */
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 4ae31b7af6c3..3831c1a97f79 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -5,6 +5,7 @@
  * Original Copyright (C) 1995  Linus Torvalds
  * Copyright (C) 1996-2000 Russell King - Converted to ARM.
  * Copyright (C) 2012 ARM Ltd.
+ * Copyright © 2024 Apple Inc. All rights reserved.
  */
 #include <linux/compat.h>
 #include <linux/efi.h>
@@ -55,6 +56,7 @@
 #include <asm/stacktrace.h>
 #include <asm/switch_to.h>
 #include <asm/system_misc.h>
+#include <asm/tso.h>
 
 #if defined(CONFIG_STACKPROTECTOR) && !defined(CONFIG_STACKPROTECTOR_PER_TASK)
 #include <linux/stackprotector.h>
@@ -530,6 +532,9 @@ struct task_struct *__switch_to(struct task_struct *prev,
 	ssbs_thread_switch(next);
 	erratum_1418040_thread_switch(next);
 	ptrauth_thread_switch_user(next);
+#ifdef CONFIG_ARM64_TSO
+	tso_thread_switch(next);
+#endif
 
 	/*
 	 * Complete any pending TLB or cache maintenance on this CPU in case
@@ -651,6 +656,10 @@ void arch_setup_new_exec(void)
 		arch_prctl_spec_ctrl_set(current, PR_SPEC_STORE_BYPASS,
 					 PR_SPEC_ENABLE);
 	}
+
+#ifdef CONFIG_ARM64_TSO
+	modify_tso_enable(false);
+#endif
 }
 
 #ifdef CONFIG_ARM64_TAGGED_ADDR_ABI
diff --git a/arch/arm64/kernel/tso.c b/arch/arm64/kernel/tso.c
index b3964db7aa66..9a15d825943f 100644
--- a/arch/arm64/kernel/tso.c
+++ b/arch/arm64/kernel/tso.c
@@ -3,6 +3,7 @@
  * Copyright © 2024 Apple Inc. All rights reserved.
  */
 
+#include <linux/sched.h>
 #include <linux/types.h>
 
 #include <asm/cputype.h>
@@ -49,4 +50,12 @@ int modify_tso_enable(bool tso_enable)
 	return 0;
 }
 
+void tso_thread_switch(struct task_struct *next)
+{
+	if (tso_supported()) {
+		current->thread.tso = tso_enabled();
+		modify_tso_enable(next->thread.tso);
+	}
+}
+
 #endif /* CONFIG_ARM64_TSO */
-- 
2.39.3 (Apple Git-146)