Subject: [RFC PATCH 1/7] asm-generic: add generic MMU versions of mmu context functions

From: Nicholas Piggin <[email-masked]>
Date: Fri, 10 Jul 2020 11:56:40 +1000

Many of these are no-ops on many architectures, so extend mmu_context.h
to cover MMU and NOMMU, and split the NOMMU bits out to nommu_context.h

Cc: Arnd Bergmann <[email-masked]>
Cc: Remis Lima Baima <[email-masked]>
Signed-off-by: Nicholas Piggin <[email-masked]>
---
 arch/microblaze/include/asm/mmu_context.h |  2 +-
 arch/sh/include/asm/mmu_context.h         |  2 +-
 include/asm-generic/mmu_context.h         | 57 +++++++++++++++++------
 include/asm-generic/nommu_context.h       | 19 ++++++++
 4 files changed, 64 insertions(+), 16 deletions(-)
 create mode 100644 include/asm-generic/nommu_context.h

diff --git a/arch/microblaze/include/asm/mmu_context.h b/arch/microblaze/include/asm/mmu_context.h
index f74f9da07fdc..34004efb3def 100644
--- a/arch/microblaze/include/asm/mmu_context.h
+++ b/arch/microblaze/include/asm/mmu_context.h
@@ -2,5 +2,5 @@
 #ifdef CONFIG_MMU
 # include <asm/mmu_context_mm.h>
 #else
-# include <asm-generic/mmu_context.h>
+# include <asm-generic/nommu_context.h>
 #endif
diff --git a/arch/sh/include/asm/mmu_context.h b/arch/sh/include/asm/mmu_context.h
index 48e67d544d53..9470d17c71c2 100644
--- a/arch/sh/include/asm/mmu_context.h
+++ b/arch/sh/include/asm/mmu_context.h
@@ -134,7 +134,7 @@ static inline void switch_mm(struct mm_struct *prev,
 #define set_TTB(pgd)			do { } while (0)
 #define get_TTB()			(0)
 
-#include <asm-generic/mmu_context.h>
+#include <asm-generic/nommu_context.h>
 
 #endif /* CONFIG_MMU */
 
diff --git a/include/asm-generic/mmu_context.h b/include/asm-generic/mmu_context.h
index 6be9106fb6fb..86cea80a50df 100644
--- a/include/asm-generic/mmu_context.h
+++ b/include/asm-generic/mmu_context.h
@@ -3,44 +3,73 @@
 #define __ASM_GENERIC_MMU_CONTEXT_H
 
 /*
- * Generic hooks for NOMMU architectures, which do not need to do
- * anything special here.
+ * Generic hooks to implement no-op functionality.
  */
 
-#include <asm-generic/mm_hooks.h>
-
 struct task_struct;
 struct mm_struct;
 
+/*
+ * enter_lazy_tlb - Called when "tsk" is about to enter lazy TLB mode.
+ *
+ * @mm:  the currently active mm context which is becoming lazy
+ * @tsk: task which is entering lazy tlb
+ *
+ * tsk->mm will be NULL
+ */
+#ifndef enter_lazy_tlb
 static inline void enter_lazy_tlb(struct mm_struct *mm,
 			struct task_struct *tsk)
 {
 }
+#endif
 
+/**
+ * init_new_context - Initialize context of a new mm_struct.
+ * @tsk: task struct for the mm
+ * @mm:  the new mm struct
+ */
+#ifndef init_new_context
 static inline int init_new_context(struct task_struct *tsk,
 			struct mm_struct *mm)
 {
 	return 0;
 }
+#endif
 
+/**
+ * destroy_context - Undo init_new_context when the mm is going away
+ * @mm: old mm struct
+ */
+#ifndef destroy_context
 static inline void destroy_context(struct mm_struct *mm)
 {
 }
+#endif
 
-static inline void deactivate_mm(struct task_struct *task,
-			struct mm_struct *mm)
-{
-}
-
-static inline void switch_mm(struct mm_struct *prev,
-			struct mm_struct *next,
-			struct task_struct *tsk)
+/**
+ * activate_mm - called after exec switches the current task to a new mm, to switch to it
+ * @prev_mm: previous mm of this task
+ * @next_mm: new mm
+ */
+#ifndef activate_mm
+static inline void activate_mm(struct mm_struct *prev_mm,
+			       struct mm_struct *next_mm)
 {
+	switch_mm(prev_mm, next_mm, current);
 }
+#endif
 
-static inline void activate_mm(struct mm_struct *prev_mm,
-			       struct mm_struct *next_mm)
+/**
+ * dectivate_mm - called when an mm is released after exit or exec switches away from it
+ * @tsk: the task
+ * @mm:  the old mm
+ */
+#ifndef deactivate_mm
+static inline void deactivate_mm(struct task_struct *tsk,
+			struct mm_struct *mm)
 {
 }
+#endif
 
 #endif /* __ASM_GENERIC_MMU_CONTEXT_H */
diff --git a/include/asm-generic/nommu_context.h b/include/asm-generic/nommu_context.h
new file mode 100644
index 000000000000..72b8d8b1d81e
--- /dev/null
+++ b/include/asm-generic/nommu_context.h
@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_GENERIC_NOMMU_H
+#define __ASM_GENERIC_NOMMU_H
+
+/*
+ * Generic hooks for NOMMU architectures, which do not need to do
+ * anything special here.
+ */
+
+#include <asm-generic/mm_hooks.h>
+#include <asm-generic/mmu_context.h>
+
+static inline void switch_mm(struct mm_struct *prev,
+			struct mm_struct *next,
+			struct task_struct *tsk)
+{
+}
+
+#endif /* __ASM_GENERIC_NOMMU_H */
-- 
2.23.0