mm, powerpc: move the RCU page-table freeing into generic code

In case other architectures require RCU freed page-tables to implement
gup_fast() and software filled hashes and similar things, provide the
means to do so by moving the logic into generic code.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Requested-by: David Miller <davem@davemloft.net>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: Tony Luck <tony.luck@intel.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Nick Piggin <npiggin@kernel.dk>
Cc: Namhyung Kim <namhyung@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

10 files changed, 150 insertions, 125 deletions

diff --git a/arch/Kconfig b/arch/Kconfig
index 8d24bacaa61e..26b0e2397a57 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -175,4 +175,7 @@ config HAVE_ARCH_JUMP_LABEL
 config HAVE_ARCH_MUTEX_CPU_RELAX
         bool
 
+config HAVE_RCU_TABLE_FREE
+        bool
+
 source "kernel/gcov/Kconfig"
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index a3128ca0fe11..423145a6f7ba 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -140,6 +140,7 @@ config PPC
         select IRQ_PER_CPU
         select GENERIC_IRQ_SHOW
         select GENERIC_IRQ_SHOW_LEVEL
+        select HAVE_RCU_TABLE_FREE if SMP
 
 config EARLY_PRINTK
         bool
diff --git a/arch/powerpc/include/asm/pgalloc.h b/arch/powerpc/include/asm/pgalloc.h
index df1b4cbb2e70..bf301ac62f35 100644
--- a/arch/powerpc/include/asm/pgalloc.h
+++ b/arch/powerpc/include/asm/pgalloc.h
@@ -31,14 +31,29 @@ static inline void pte_free(struct mm_struct *mm, pgtable_t ptepage)
 #endif
 
 #ifdef CONFIG_SMP
-extern void pgtable_free_tlb(struct mmu_gather *tlb, void *table, unsigned shift);
-extern void pte_free_finish(struct mmu_gather *tlb);
+struct mmu_gather;
+extern void tlb_remove_table(struct mmu_gather *, void *);
+
+static inline void pgtable_free_tlb(struct mmu_gather *tlb, void *table, int shift)
+{
+        unsigned long pgf = (unsigned long)table;
+        BUG_ON(shift > MAX_PGTABLE_INDEX_SIZE);
+        pgf |= shift;
+        tlb_remove_table(tlb, (void *)pgf);
+}
+
+static inline void __tlb_remove_table(void *_table)
+{
+        void *table = (void *)((unsigned long)_table & ~MAX_PGTABLE_INDEX_SIZE);
+        unsigned shift = (unsigned long)_table & MAX_PGTABLE_INDEX_SIZE;
+
+        pgtable_free(table, shift);
+}
 #else /* CONFIG_SMP */
 static inline void pgtable_free_tlb(struct mmu_gather *tlb, void *table, unsigned shift)
 {
         pgtable_free(table, shift);
 }
-static inline void pte_free_finish(struct mmu_gather *tlb) { }
 #endif /* !CONFIG_SMP */
 
 static inline void __pte_free_tlb(struct mmu_gather *tlb, struct page *ptepage,
diff --git a/arch/powerpc/include/asm/tlb.h b/arch/powerpc/include/asm/tlb.h
index 8f0ed7adcd12..e2b428b0f7ba 100644
--- a/arch/powerpc/include/asm/tlb.h
+++ b/arch/powerpc/include/asm/tlb.h
@@ -28,16 +28,6 @@
 #define tlb_start_vma(tlb, vma) do { } while (0)
 #define tlb_end_vma(tlb, vma)   do { } while (0)
 
-#define HAVE_ARCH_MMU_GATHER 1
-
-struct pte_freelist_batch;
-
-struct arch_mmu_gather {
-        struct pte_freelist_batch *batch;
-};
-
-#define ARCH_MMU_GATHER_INIT (struct arch_mmu_gather){ .batch = NULL, }
-
 extern void tlb_flush(struct mmu_gather *tlb);
 
 /* Get the generic bits... */
diff --git a/arch/powerpc/mm/pgtable.c b/arch/powerpc/mm/pgtable.c
index 6e72788598f8..af40c8768a78 100644
--- a/arch/powerpc/mm/pgtable.c
+++ b/arch/powerpc/mm/pgtable.c
@@ -33,104 +33,6 @@
 
 #include "mmu_decl.h"
 
-#ifdef CONFIG_SMP
-
-/*
- * Handle batching of page table freeing on SMP. Page tables are
- * queued up and send to be freed later by RCU in order to avoid
- * freeing a page table page that is being walked without locks
- */
-
-static unsigned long pte_freelist_forced_free;
-
-struct pte_freelist_batch
-{
-        struct rcu_head rcu;
-        unsigned int    index;
-        unsigned long   tables[0];
-};
-
-#define PTE_FREELIST_SIZE \
-        ((PAGE_SIZE - sizeof(struct pte_freelist_batch)) \
-          / sizeof(unsigned long))
-
-static void pte_free_smp_sync(void *arg)
-{
-        /* Do nothing, just ensure we sync with all CPUs */
-}
-
-/* This is only called when we are critically out of memory
- * (and fail to get a page in pte_free_tlb).
- */
-static void pgtable_free_now(void *table, unsigned shift)
-{
-        pte_freelist_forced_free++;
-
-        smp_call_function(pte_free_smp_sync, NULL, 1);
-
-        pgtable_free(table, shift);
-}
-
-static void pte_free_rcu_callback(struct rcu_head *head)
-{
-        struct pte_freelist_batch *batch =
-                container_of(head, struct pte_freelist_batch, rcu);
-        unsigned int i;
-
-        for (i = 0; i < batch->index; i++) {
-                void *table = (void *)(batch->tables[i] & ~MAX_PGTABLE_INDEX_SIZE);
-                unsigned shift = batch->tables[i] & MAX_PGTABLE_INDEX_SIZE;
-
-                pgtable_free(table, shift);
-        }
-
-        free_page((unsigned long)batch);
-}
-
-static void pte_free_submit(struct pte_freelist_batch *batch)
-{
-        call_rcu_sched(&batch->rcu, pte_free_rcu_callback);
-}
-
-void pgtable_free_tlb(struct mmu_gather *tlb, void *table, unsigned shift)
-{
-        struct pte_freelist_batch **batchp = &tlb->arch.batch;
-        unsigned long pgf;
-
-        if (atomic_read(&tlb->mm->mm_users) < 2) {
-                pgtable_free(table, shift);
-                return;
-        }
-
-        if (*batchp == NULL) {
-                *batchp = (struct pte_freelist_batch *)__get_free_page(GFP_ATOMIC);
-                if (*batchp == NULL) {
-                        pgtable_free_now(table, shift);
-                        return;
-                }
-                (*batchp)->index = 0;
-        }
-        BUG_ON(shift > MAX_PGTABLE_INDEX_SIZE);
-        pgf = (unsigned long)table | shift;
-        (*batchp)->tables[(*batchp)->index++] = pgf;
-        if ((*batchp)->index == PTE_FREELIST_SIZE) {
-                pte_free_submit(*batchp);
-                *batchp = NULL;
-        }
-}
-
-void pte_free_finish(struct mmu_gather *tlb)
-{
-        struct pte_freelist_batch **batchp = &tlb->arch.batch;
-
-        if (*batchp == NULL)
-                return;
-        pte_free_submit(*batchp);
-        *batchp = NULL;
-}
-
-#endif /* CONFIG_SMP */
-
 static inline int is_exec_fault(void)
 {
         return current->thread.regs && TRAP(current->thread.regs) == 0x400;
diff --git a/arch/powerpc/mm/tlb_hash32.c b/arch/powerpc/mm/tlb_hash32.c
index d555cdb06bc8..27b863c14941 100644
--- a/arch/powerpc/mm/tlb_hash32.c
+++ b/arch/powerpc/mm/tlb_hash32.c
@@ -71,9 +71,6 @@ void tlb_flush(struct mmu_gather *tlb)
                  */
                 _tlbia();
         }
-
-        /* Push out batch of freed page tables */
-        pte_free_finish(tlb);
 }
 
 /*
diff --git a/arch/powerpc/mm/tlb_hash64.c b/arch/powerpc/mm/tlb_hash64.c
index 5c94ca34cd79..31f18207970b 100644
--- a/arch/powerpc/mm/tlb_hash64.c
+++ b/arch/powerpc/mm/tlb_hash64.c
@@ -165,9 +165,6 @@ void tlb_flush(struct mmu_gather *tlb)
                 __flush_tlb_pending(tlbbatch);
 
         put_cpu_var(ppc64_tlb_batch);
-
-        /* Push out batch of freed page tables */
-        pte_free_finish(tlb);
 }
 
 /**
diff --git a/arch/powerpc/mm/tlb_nohash.c b/arch/powerpc/mm/tlb_nohash.c
index 8eaf67d32043..0bdad3aecc67 100644
--- a/arch/powerpc/mm/tlb_nohash.c
+++ b/arch/powerpc/mm/tlb_nohash.c
@@ -299,9 +299,6 @@ EXPORT_SYMBOL(flush_tlb_range);
 void tlb_flush(struct mmu_gather *tlb)
 {
         flush_tlb_mm(tlb->mm);
-
-        /* Push out batch of freed page tables */
-        pte_free_finish(tlb);
 }
 
 /*
diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h
index 2d3547c84235..74f80f6b6cf1 100644
--- a/include/asm-generic/tlb.h
+++ b/include/asm-generic/tlb.h
@@ -29,6 +29,49 @@
   #define tlb_fast_mode(tlb) 1
 #endif
 
+#ifdef CONFIG_HAVE_RCU_TABLE_FREE
+/*
+ * Semi RCU freeing of the page directories.
+ *
+ * This is needed by some architectures to implement software pagetable walkers.
+ *
+ * gup_fast() and other software pagetable walkers do a lockless page-table
+ * walk and therefore needs some synchronization with the freeing of the page
+ * directories. The chosen means to accomplish that is by disabling IRQs over
+ * the walk.
+ *
+ * Architectures that use IPIs to flush TLBs will then automagically DTRT,
+ * since we unlink the page, flush TLBs, free the page. Since the disabling of
+ * IRQs delays the completion of the TLB flush we can never observe an already
+ * freed page.
+ *
+ * Architectures that do not have this (PPC) need to delay the freeing by some
+ * other means, this is that means.
+ *
+ * What we do is batch the freed directory pages (tables) and RCU free them.
+ * We use the sched RCU variant, as that guarantees that IRQ/preempt disabling
+ * holds off grace periods.
+ *
+ * However, in order to batch these pages we need to allocate storage, this
+ * allocation is deep inside the MM code and can thus easily fail on memory
+ * pressure. To guarantee progress we fall back to single table freeing, see
+ * the implementation of tlb_remove_table_one().
+ *
+ */
+struct mmu_table_batch {
+        struct rcu_head         rcu;
+        unsigned int            nr;
+        void                    *tables[0];
+};
+
+#define MAX_TABLE_BATCH         \
+        ((PAGE_SIZE - sizeof(struct mmu_table_batch)) / sizeof(void *))
+
+extern void tlb_table_flush(struct mmu_gather *tlb);
+extern void tlb_remove_table(struct mmu_gather *tlb, void *table);
+
+#endif
+
 /*
  * If we can't allocate a page to make a big batch of page pointers
  * to work on, then just handle a few from the on-stack structure.
@@ -40,13 +83,13 @@
  */
 struct mmu_gather {
         struct mm_struct        *mm;
+#ifdef CONFIG_HAVE_RCU_TABLE_FREE
+        struct mmu_table_batch  *batch;
+#endif
         unsigned int            nr;     /* set to ~0U means fast mode */
         unsigned int            max;    /* nr < max */
         unsigned int            need_flush;/* Really unmapped some ptes? */
         unsigned int            fullmm; /* non-zero means full mm flush */
-#ifdef HAVE_ARCH_MMU_GATHER
-        struct arch_mmu_gather  arch;
-#endif
         struct page             **pages;
         struct page             *local[MMU_GATHER_BUNDLE];
 };
@@ -82,8 +125,8 @@ tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm, bool fullmm)
 
         tlb->fullmm = fullmm;
 
-#ifdef HAVE_ARCH_MMU_GATHER
-        tlb->arch = ARCH_MMU_GATHER_INIT;
+#ifdef CONFIG_HAVE_RCU_TABLE_FREE
+        tlb->batch = NULL;
 #endif
 }
 
@@ -94,6 +137,9 @@ tlb_flush_mmu(struct mmu_gather *tlb)
                 return;
         tlb->need_flush = 0;
         tlb_flush(tlb);
+#ifdef CONFIG_HAVE_RCU_TABLE_FREE
+        tlb_table_flush(tlb);
+#endif
         if (!tlb_fast_mode(tlb)) {
                 free_pages_and_swap_cache(tlb->pages, tlb->nr);
                 tlb->nr = 0;
diff --git a/mm/memory.c b/mm/memory.c
index 19b2d44de9f0..a77fd23ee68a 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -193,6 +193,83 @@ static void check_sync_rss_stat(struct task_struct *task)
 
 #endif
 
+#ifdef CONFIG_HAVE_RCU_TABLE_FREE
+
+/*
+ * See the comment near struct mmu_table_batch.
+ */
+
+static void tlb_remove_table_smp_sync(void *arg)
+{
+        /* Simply deliver the interrupt */
+}
+
+static void tlb_remove_table_one(void *table)
+{
+        /*
+         * This isn't an RCU grace period and hence the page-tables cannot be
+         * assumed to be actually RCU-freed.
+         *
+         * It is however sufficient for software page-table walkers that rely on
+         * IRQ disabling. See the comment near struct mmu_table_batch.
+         */
+        smp_call_function(tlb_remove_table_smp_sync, NULL, 1);
+        __tlb_remove_table(table);
+}
+
+static void tlb_remove_table_rcu(struct rcu_head *head)
+{
+        struct mmu_table_batch *batch;
+        int i;
+
+        batch = container_of(head, struct mmu_table_batch, rcu);
+
+        for (i = 0; i < batch->nr; i++)
+                __tlb_remove_table(batch->tables[i]);
+
+        free_page((unsigned long)batch);
+}
+
+void tlb_table_flush(struct mmu_gather *tlb)
+{
+        struct mmu_table_batch **batch = &tlb->batch;
+
+        if (*batch) {
+                call_rcu_sched(&(*batch)->rcu, tlb_remove_table_rcu);
+                *batch = NULL;
+        }
+}
+
+void tlb_remove_table(struct mmu_gather *tlb, void *table)
+{
+        struct mmu_table_batch **batch = &tlb->batch;
+
+        tlb->need_flush = 1;
+
+        /*
+         * When there's less then two users of this mm there cannot be a
+         * concurrent page-table walk.
+         */
+        if (atomic_read(&tlb->mm->mm_users) < 2) {
+                __tlb_remove_table(table);
+                return;
+        }
+
+        if (*batch == NULL) {
+                *batch = (struct mmu_table_batch *)__get_free_page(GFP_NOWAIT | __GFP_NOWARN);
+                if (*batch == NULL) {
+                        tlb_remove_table_one(table);
+                        return;
+                }
+                (*batch)->nr = 0;
+        }
+        (*batch)->tables[(*batch)->nr++] = table;
+        if ((*batch)->nr == MAX_TABLE_BATCH)
+                tlb_table_flush(tlb);
+}
+
+#endif
+
 /*
  * If a p?d_bad entry is found while walking page tables, report
  * the error, before resetting entry to p?d_none.  Usually (but