[PATCH v4 5/9] mm/mmu_notifier: mmu_notifier_range_update_to_read_only() helper

[jglisse at redhat.com]

From: Jérôme Glisse <jglisse at redhat.com>

Helper to test if a range is updated to read only (it is still valid
to read from the range). This is useful for device driver or anyone
who wish to optimize out update when they know that they already have
the range map read only.

Signed-off-by: Jérôme Glisse <jglisse at redhat.com>
Cc: Christian König <christian.koenig at amd.com>
Cc: Jan Kara <jack at suse.cz>
Cc: Felix Kuehling <Felix.Kuehling at amd.com>
Cc: Jason Gunthorpe <jgg at mellanox.com>
Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: Matthew Wilcox <mawilcox at microsoft.com>
Cc: Ross Zwisler <zwisler at kernel.org>
Cc: Dan Williams <dan.j.williams at intel.com>
Cc: Paolo Bonzini <pbonzini at redhat.com>
Cc: Radim Krčmář <rkrcmar at redhat.com>
Cc: Michal Hocko <mhocko at kernel.org>
Cc: Ralph Campbell <rcampbell at nvidia.com>
Cc: John Hubbard <jhubbard at nvidia.com>
Cc: kvm at vger.kernel.org
Cc: dri-devel at lists.freedesktop.org
Cc: linux-rdma at vger.kernel.org
Cc: linux-fsdevel at vger.kernel.org
Cc: Arnd Bergmann <arnd at arndb.de>
---
 include/linux/mmu_notifier.h |  4 ++++
 mm/mmu_notifier.c            | 10 ++++++++++
 2 files changed, 14 insertions(+)

diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h
index 7514775817de..be873c431886 100644
--- a/include/linux/mmu_notifier.h
+++ b/include/linux/mmu_notifier.h
@@ -257,6 +257,8 @@ extern void __mmu_notifier_invalidate_range_end(struct mmu_notifier_range *r,
 				  bool only_end);
 extern void __mmu_notifier_invalidate_range(struct mm_struct *mm,
 				  unsigned long start, unsigned long end);
+extern bool
+mmu_notifier_range_update_to_read_only(const struct mmu_notifier_range *range);
 
 static inline void mmu_notifier_release(struct mm_struct *mm)
 {
@@ -553,6 +555,8 @@ static inline void mmu_notifier_mm_destroy(struct mm_struct *mm)
 {
 }
 
+#define mmu_notifier_range_update_to_read_only(r) false
+
 #define ptep_clear_flush_young_notify ptep_clear_flush_young
 #define pmdp_clear_flush_young_notify pmdp_clear_flush_young
 #define ptep_clear_young_notify ptep_test_and_clear_young
diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c
index 9c884abc7850..0b2f77715a08 100644
--- a/mm/mmu_notifier.c
+++ b/mm/mmu_notifier.c
@@ -395,3 +395,13 @@ void mmu_notifier_unregister_no_release(struct mmu_notifier *mn,
 	mmdrop(mm);
 }
 EXPORT_SYMBOL_GPL(mmu_notifier_unregister_no_release);
+
+bool
+mmu_notifier_range_update_to_read_only(const struct mmu_notifier_range *range)
+{
+	if (!range->vma || range->event != MMU_NOTIFY_PROTECTION_VMA)
+		return false;
+	/* Return true if the vma still have the read flag set. */
+	return range->vma->vm_flags & VM_READ;
+}
+EXPORT_SYMBOL_GPL(mmu_notifier_range_update_to_read_only);
-- 
2.17.2