[PATCH 01/10] ksm: add mmu_notifier set_pte_at_notify()

[Izik Eidus]

From: Izik Eidus <ieidus@xxxxxxxxxx>

The set_pte_at_notify() macro allows setting a pte in the shadow page
table directly, instead of flushing the shadow page table entry and then
getting vmexit to set it.  It uses a new change_pte() callback to do so.

set_pte_at_notify() is an optimization for kvm, and other users of
mmu_notifiers, for COW pages.  It is useful for kvm when ksm is used,
because it allows kvm not to have to receive vmexit and only then map
the ksm page into the shadow page table, but instead map it directly
at the same time as Linux maps the page into the host page table.

Users of mmu_notifiers who don't implement new mmu_notifier_change_pte()
callback will just receive the mmu_notifier_invalidate_page() callback.

Signed-off-by: Izik Eidus <ieidus@xxxxxxxxxx>
Signed-off-by: Chris Wright <chrisw@xxxxxxxxxx>
Signed-off-by: Hugh Dickins <hugh.dickins@xxxxxxxxxxxxx>
---
 include/linux/mmu_notifier.h |   34 ++++++++++++++++++++++++++++++++++
 mm/memory.c                  |    9 +++++++--
 mm/mmu_notifier.c            |   20 ++++++++++++++++++++
 3 files changed, 61 insertions(+), 2 deletions(-)

diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h
index b77486d..4e02ee2 100644
--- a/include/linux/mmu_notifier.h
+++ b/include/linux/mmu_notifier.h
@@ -62,6 +62,15 @@ struct mmu_notifier_ops {
 				 unsigned long address);
 
 	/*
+	 * change_pte is called in cases that pte mapping to page is changed:
+	 * for example, when ksm remaps pte to point to a new shared page.
+	 */
+	void (*change_pte)(struct mmu_notifier *mn,
+			   struct mm_struct *mm,
+			   unsigned long address,
+			   pte_t pte);
+
+	/*
 	 * Before this is invoked any secondary MMU is still ok to
 	 * read/write to the page previously pointed to by the Linux
 	 * pte because the page hasn't been freed yet and it won't be
@@ -154,6 +163,8 @@ extern void __mmu_notifier_mm_destroy(struct mm_struct *mm);
 extern void __mmu_notifier_release(struct mm_struct *mm);
 extern int __mmu_notifier_clear_flush_young(struct mm_struct *mm,
 					  unsigned long address);
+extern void __mmu_notifier_change_pte(struct mm_struct *mm,
+				      unsigned long address, pte_t pte);
 extern void __mmu_notifier_invalidate_page(struct mm_struct *mm,
 					  unsigned long address);
 extern void __mmu_notifier_invalidate_range_start(struct mm_struct *mm,
@@ -175,6 +186,13 @@ static inline int mmu_notifier_clear_flush_young(struct mm_struct *mm,
 	return 0;
 }
 
+static inline void mmu_notifier_change_pte(struct mm_struct *mm,
+					   unsigned long address, pte_t pte)
+{
+	if (mm_has_notifiers(mm))
+		__mmu_notifier_change_pte(mm, address, pte);
+}
+
 static inline void mmu_notifier_invalidate_page(struct mm_struct *mm,
 					  unsigned long address)
 {
@@ -236,6 +254,16 @@ static inline void mmu_notifier_mm_destroy(struct mm_struct *mm)
 	__young;							\
 })
 
+#define set_pte_at_notify(__mm, __address, __ptep, __pte)		\
+({									\
+	struct mm_struct *___mm = __mm;					\
+	unsigned long ___address = __address;				\
+	pte_t ___pte = __pte;						\
+									\
+	set_pte_at(___mm, ___address, __ptep, ___pte);			\
+	mmu_notifier_change_pte(___mm, ___address, ___pte);		\
+})
+
 #else /* CONFIG_MMU_NOTIFIER */
 
 static inline void mmu_notifier_release(struct mm_struct *mm)
@@ -248,6 +276,11 @@ static inline int mmu_notifier_clear_flush_young(struct mm_struct *mm,
 	return 0;
 }
 
+static inline void mmu_notifier_change_pte(struct mm_struct *mm,
+					   unsigned long address, pte_t pte)
+{
+}
+
 static inline void mmu_notifier_invalidate_page(struct mm_struct *mm,
 					  unsigned long address)
 {
@@ -273,6 +306,7 @@ static inline void mmu_notifier_mm_destroy(struct mm_struct *mm)
 
 #define ptep_clear_flush_young_notify ptep_clear_flush_young
 #define ptep_clear_flush_notify ptep_clear_flush
+#define set_pte_at_notify set_pte_at
 
 #endif /* CONFIG_MMU_NOTIFIER */
 
diff --git a/mm/memory.c b/mm/memory.c
index 6521619..8159a62 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2113,9 +2113,14 @@ gotten:
 		 * seen in the presence of one thread doing SMC and another
 		 * thread doing COW.
 		 */
-		ptep_clear_flush_notify(vma, address, page_table);
+		ptep_clear_flush(vma, address, page_table);
 		page_add_new_anon_rmap(new_page, vma, address);
-		set_pte_at(mm, address, page_table, entry);
+		/*
+		 * We call the notify macro here because, when using secondary
+		 * mmu page tables (such as kvm shadow page tables), we want the
+		 * new page to be mapped directly into the secondary page table.
+		 */
+		set_pte_at_notify(mm, address, page_table, entry);
 		update_mmu_cache(vma, address, entry);
 		if (old_page) {
 			/*
diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c
index 5f4ef02..7e33f2c 100644
--- a/mm/mmu_notifier.c
+++ b/mm/mmu_notifier.c
@@ -99,6 +99,26 @@ int __mmu_notifier_clear_flush_young(struct mm_struct *mm,
 	return young;
 }
 
+void __mmu_notifier_change_pte(struct mm_struct *mm, unsigned long address,
+			       pte_t pte)
+{
+	struct mmu_notifier *mn;
+	struct hlist_node *n;
+
+	rcu_read_lock();
+	hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
+		if (mn->ops->change_pte)
+			mn->ops->change_pte(mn, mm, address, pte);
+		/*
+		 * Some drivers don't have change_pte,
+		 * so we must call invalidate_page in that case.
+		 */
+		else if (mn->ops->invalidate_page)
+			mn->ops->invalidate_page(mn, mm, address);
+	}
+	rcu_read_unlock();
+}
+
 void __mmu_notifier_invalidate_page(struct mm_struct *mm,
 					  unsigned long address)
 {
-- 
1.5.6.5

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