tlb: mmu_gather: Introduce tlb_gather_mmu_fullmm()

Passing the range '0, -1' to tlb_gather_mmu() sets the 'fullmm' flag,
which indicates that the mm_struct being operated on is going away. In
this case, some architectures (such as arm64) can elide TLB invalidation
by ensuring that the TLB tag (ASID) associated with this mm is not
immediately reclaimed. Although this behaviour is documented in
asm-generic/tlb.h, it's subtle and easily missed.

Introduce tlb_gather_mmu_fullmm() to make it clearer that this is for the
entire mm and WARN() if tlb_gather_mmu() is called with the 'fullmm'
address range.

Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Yu Zhao <yuzhao@google.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lkml.kernel.org/r/20210127235347.1402-4-will@kernel.org

diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h
index 6661ee1cff479ffb5297be5a001625d03b517f85..2c68a545ffa7d2a5c743da5f57e8e46367a910d2 100644 (file)
--- a/include/asm-generic/tlb.h
+++ b/include/asm-generic/tlb.h
@@ -46,7 +46,9 @@
  *
  * The mmu_gather API consists of:
  *
- *  - tlb_gather_mmu() / tlb_finish_mmu(); start and finish a mmu_gather
+ *  - tlb_gather_mmu() / tlb_gather_mmu_fullmm() / tlb_finish_mmu()
+ *
+ *    start and finish a mmu_gather
  *
  *    Finish in particular will issue a (final) TLB invalidate and free
  *    all (remaining) queued pages.
@@ -91,7 +93,7 @@
  *
  *  - mmu_gather::fullmm
  *
- *    A flag set by tlb_gather_mmu() to indicate we're going to free
+ *    A flag set by tlb_gather_mmu_fullmm() to indicate we're going to free
  *    the entire mm; this allows a number of optimizations.
  *
  *    - We can ignore tlb_{start,end}_vma(); because we don't

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 1fe6a51298a682c16616c3ded1b4e155ff3b90e6..e49868bc12a75beda6e884fc4ef282934141f63d 100644 (file)
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -590,6 +590,7 @@ static inline cpumask_t *mm_cpumask(struct mm_struct *mm)
 struct mmu_gather;
 extern void tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm,
                                unsigned long start, unsigned long end);
+extern void tlb_gather_mmu_fullmm(struct mmu_gather *tlb, struct mm_struct *mm);
 extern void tlb_finish_mmu(struct mmu_gather *tlb);
 
 static inline void init_tlb_flush_pending(struct mm_struct *mm)

diff --git a/mm/mmap.c b/mm/mmap.c
index 7a9f493a4b83a376896c3ba2fcfff74c9eba0f15..4eac7c63edbe7550e21558db04cbc2cfdc954b50 100644 (file)
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -3214,7 +3214,7 @@ void exit_mmap(struct mm_struct *mm)
 
        lru_add_drain();
        flush_cache_mm(mm);
-       tlb_gather_mmu(&tlb, mm, 0, -1);
+       tlb_gather_mmu_fullmm(&tlb, mm);
        /* update_hiwater_rss(mm) here? but nobody should be looking */
        /* Use -1 here to ensure all VMAs in the mm are unmapped */
        unmap_vmas(&tlb, vma, 0, -1);

diff --git a/mm/mmu_gather.c b/mm/mmu_gather.c
index b0be5a7aa08f6d054c5f69bd4af4e95955d2192b..5f5e45d9eb50d78d96d1915e4f0b4e7126f2d256 100644 (file)
--- a/mm/mmu_gather.c
+++ b/mm/mmu_gather.c
@@ -261,8 +261,8 @@ void tlb_flush_mmu(struct mmu_gather *tlb)
  * respectively when @mm is without users and we're going to destroy
  * the full address space (exit/execve).
  */
-void tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm,
-                       unsigned long start, unsigned long end)
+static void __tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm,
+                            unsigned long start, unsigned long end)
 {
        tlb->mm = mm;
 
@@ -287,6 +287,18 @@ void tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm,
        inc_tlb_flush_pending(tlb->mm);
 }
 
+void tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm,
+                   unsigned long start, unsigned long end)
+{
+       WARN_ON(!(start | (end + 1))); /* Use _fullmm() instead */
+       __tlb_gather_mmu(tlb, mm, start, end);
+}
+
+void tlb_gather_mmu_fullmm(struct mmu_gather *tlb, struct mm_struct *mm)
+{
+       __tlb_gather_mmu(tlb, mm, 0, -1);
+}
+
 /**
  * tlb_finish_mmu - finish an mmu_gather structure
  * @tlb: the mmu_gather structure to finish