[S390] use generic RCU page-table freeing code

Replace the s390 specific rcu page-table freeing code with the
generic variant. This requires to duplicate the definition for the
struct mmu_table_batch as s390 does not use the generic tlb flush
code.

While we are at it remove the restriction that page table fragments
can not be reused after a single fragment has been freed with rcu
and split out allocation and freeing of page tables with pgstes.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

4 files changed, 166 insertions, 229 deletions

diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index 9fab2aa9c2c..90d77bd078f 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -89,6 +89,7 @@ config S390
         select HAVE_GET_USER_PAGES_FAST
         select HAVE_ARCH_MUTEX_CPU_RELAX
         select HAVE_ARCH_JUMP_LABEL if !MARCH_G5
+        select HAVE_RCU_TABLE_FREE if SMP
         select ARCH_INLINE_SPIN_TRYLOCK
         select ARCH_INLINE_SPIN_TRYLOCK_BH
         select ARCH_INLINE_SPIN_LOCK
diff --git a/arch/s390/include/asm/pgalloc.h b/arch/s390/include/asm/pgalloc.h
index f6314af3b35..38e71ebcd3c 100644
--- a/arch/s390/include/asm/pgalloc.h
+++ b/arch/s390/include/asm/pgalloc.h
@@ -17,15 +17,15 @@
 #include <linux/gfp.h>
 #include <linux/mm.h>
 
-#define check_pgt_cache()       do {} while (0)
-
 unsigned long *crst_table_alloc(struct mm_struct *);
 void crst_table_free(struct mm_struct *, unsigned long *);
-void crst_table_free_rcu(struct mm_struct *, unsigned long *);
 
 unsigned long *page_table_alloc(struct mm_struct *);
 void page_table_free(struct mm_struct *, unsigned long *);
-void page_table_free_rcu(struct mm_struct *, unsigned long *);
+#ifdef CONFIG_HAVE_RCU_TABLE_FREE
+void page_table_free_rcu(struct mmu_gather *, unsigned long *);
+void __tlb_remove_table(void *_table);
+#endif
 
 static inline void clear_table(unsigned long *s, unsigned long val, size_t n)
 {
diff --git a/arch/s390/include/asm/tlb.h b/arch/s390/include/asm/tlb.h
index 77eee5477a5..c687a2c8346 100644
--- a/arch/s390/include/asm/tlb.h
+++ b/arch/s390/include/asm/tlb.h
@@ -26,67 +26,60 @@
 #include <linux/swap.h>
 #include <asm/processor.h>
 #include <asm/pgalloc.h>
-#include <asm/smp.h>
 #include <asm/tlbflush.h>
 
 struct mmu_gather {
         struct mm_struct *mm;
+#ifdef CONFIG_HAVE_RCU_TABLE_FREE
+        struct mmu_table_batch *batch;
+#endif
         unsigned int fullmm;
-        unsigned int nr_ptes;
-        unsigned int nr_pxds;
-        unsigned int max;
-        void **array;
-        void *local[8];
+        unsigned int need_flush;
 };
 
-static inline void __tlb_alloc_page(struct mmu_gather *tlb)
-{
-        unsigned long addr = __get_free_pages(GFP_NOWAIT | __GFP_NOWARN, 0);
+#ifdef CONFIG_HAVE_RCU_TABLE_FREE
+struct mmu_table_batch {
+        struct rcu_head         rcu;
+        unsigned int            nr;
+        void                    *tables[0];
+};
 
-        if (addr) {
-                tlb->array = (void *) addr;
-                tlb->max = PAGE_SIZE / sizeof(void *);
-        }
-}
+#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
 
 static inline void tlb_gather_mmu(struct mmu_gather *tlb,
                                   struct mm_struct *mm,
                                   unsigned int full_mm_flush)
 {
         tlb->mm = mm;
-        tlb->max = ARRAY_SIZE(tlb->local);
-        tlb->array = tlb->local;
         tlb->fullmm = full_mm_flush;
+        tlb->need_flush = 0;
+#ifdef CONFIG_HAVE_RCU_TABLE_FREE
+        tlb->batch = NULL;
+#endif
         if (tlb->fullmm)
                 __tlb_flush_mm(mm);
-        else
-                __tlb_alloc_page(tlb);
-        tlb->nr_ptes = 0;
-        tlb->nr_pxds = tlb->max;
 }
 
 static inline void tlb_flush_mmu(struct mmu_gather *tlb)
 {
-        if (!tlb->fullmm && (tlb->nr_ptes > 0 || tlb->nr_pxds < tlb->max))
-                __tlb_flush_mm(tlb->mm);
-        while (tlb->nr_ptes > 0)
-                page_table_free_rcu(tlb->mm, tlb->array[--tlb->nr_ptes]);
-        while (tlb->nr_pxds < tlb->max)
-                crst_table_free_rcu(tlb->mm, tlb->array[tlb->nr_pxds++]);
+        if (!tlb->need_flush)
+                return;
+        tlb->need_flush = 0;
+        __tlb_flush_mm(tlb->mm);
+#ifdef CONFIG_HAVE_RCU_TABLE_FREE
+        tlb_table_flush(tlb);
+#endif
 }
 
 static inline void tlb_finish_mmu(struct mmu_gather *tlb,
                                   unsigned long start, unsigned long end)
 {
         tlb_flush_mmu(tlb);
-
-        rcu_table_freelist_finish();
-
-        /* keep the page table cache within bounds */
-        check_pgt_cache();
-
-        if (tlb->array != tlb->local)
-                free_pages((unsigned long) tlb->array, 0);
 }
 
 /*
@@ -112,12 +105,11 @@ static inline void tlb_remove_page(struct mmu_gather *tlb, struct page *page)
 static inline void pte_free_tlb(struct mmu_gather *tlb, pgtable_t pte,
                                 unsigned long address)
 {
-        if (!tlb->fullmm) {
-                tlb->array[tlb->nr_ptes++] = pte;
-                if (tlb->nr_ptes >= tlb->nr_pxds)
-                        tlb_flush_mmu(tlb);
-        } else
-                page_table_free(tlb->mm, (unsigned long *) pte);
+#ifdef CONFIG_HAVE_RCU_TABLE_FREE
+        if (!tlb->fullmm)
+                return page_table_free_rcu(tlb, (unsigned long *) pte);
+#endif
+        page_table_free(tlb->mm, (unsigned long *) pte);
 }
 
 /*
@@ -133,12 +125,11 @@ static inline void pmd_free_tlb(struct mmu_gather *tlb, pmd_t *pmd,
 #ifdef __s390x__
         if (tlb->mm->context.asce_limit <= (1UL << 31))
                 return;
-        if (!tlb->fullmm) {
-                tlb->array[--tlb->nr_pxds] = pmd;
-                if (tlb->nr_ptes >= tlb->nr_pxds)
-                        tlb_flush_mmu(tlb);
-        } else
-                crst_table_free(tlb->mm, (unsigned long *) pmd);
+#ifdef CONFIG_HAVE_RCU_TABLE_FREE
+        if (!tlb->fullmm)
+                return tlb_remove_table(tlb, pmd);
+#endif
+        crst_table_free(tlb->mm, (unsigned long *) pmd);
 #endif
 }
 
@@ -155,12 +146,11 @@ static inline void pud_free_tlb(struct mmu_gather *tlb, pud_t *pud,
 #ifdef __s390x__
         if (tlb->mm->context.asce_limit <= (1UL << 42))
                 return;
-        if (!tlb->fullmm) {
-                tlb->array[--tlb->nr_pxds] = pud;
-                if (tlb->nr_ptes >= tlb->nr_pxds)
-                        tlb_flush_mmu(tlb);
-        } else
-                crst_table_free(tlb->mm, (unsigned long *) pud);
+#ifdef CONFIG_HAVE_RCU_TABLE_FREE
+        if (!tlb->fullmm)
+                return tlb_remove_table(tlb, pud);
+#endif
+        crst_table_free(tlb->mm, (unsigned long *) pud);
 #endif
 }
 
diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c
index b09763fe5da..37a23c22370 100644
--- a/arch/s390/mm/pgtable.c
+++ b/arch/s390/mm/pgtable.c
@@ -24,94 +24,12 @@
 #include <asm/tlbflush.h>
 #include <asm/mmu_context.h>
 
-struct rcu_table_freelist {
-        struct rcu_head rcu;
-        struct mm_struct *mm;
-        unsigned int pgt_index;
-        unsigned int crst_index;
-        unsigned long *table[0];
-};
-
-#define RCU_FREELIST_SIZE \
-        ((PAGE_SIZE - sizeof(struct rcu_table_freelist)) \
-          / sizeof(unsigned long))
-
-static DEFINE_PER_CPU(struct rcu_table_freelist *, rcu_table_freelist);
-
-static void __page_table_free(struct mm_struct *mm, unsigned long *table);
-
-static struct rcu_table_freelist *rcu_table_freelist_get(struct mm_struct *mm)
-{
-        struct rcu_table_freelist **batchp = &__get_cpu_var(rcu_table_freelist);
-        struct rcu_table_freelist *batch = *batchp;
-
-        if (batch)
-                return batch;
-        batch = (struct rcu_table_freelist *) __get_free_page(GFP_ATOMIC);
-        if (batch) {
-                batch->mm = mm;
-                batch->pgt_index = 0;
-                batch->crst_index = RCU_FREELIST_SIZE;
-                *batchp = batch;
-        }
-        return batch;
-}
-
-static void rcu_table_freelist_callback(struct rcu_head *head)
-{
-        struct rcu_table_freelist *batch =
-                container_of(head, struct rcu_table_freelist, rcu);
-
-        while (batch->pgt_index > 0)
-                __page_table_free(batch->mm, batch->table[--batch->pgt_index]);
-        while (batch->crst_index < RCU_FREELIST_SIZE)
-                crst_table_free(batch->mm, batch->table[batch->crst_index++]);
-        free_page((unsigned long) batch);
-}
-
-void rcu_table_freelist_finish(void)
-{
-        struct rcu_table_freelist **batchp = &get_cpu_var(rcu_table_freelist);
-        struct rcu_table_freelist *batch = *batchp;
-
-        if (!batch)
-                goto out;
-        call_rcu(&batch->rcu, rcu_table_freelist_callback);
-        *batchp = NULL;
-out:
-        put_cpu_var(rcu_table_freelist);
-}
-
-static void smp_sync(void *arg)
-{
-}
-
 #ifndef CONFIG_64BIT
 #define ALLOC_ORDER     1
-#define TABLES_PER_PAGE 4
-#define FRAG_MASK       15UL
-#define SECOND_HALVES   10UL
-
-void clear_table_pgstes(unsigned long *table)
-{
-        clear_table(table, _PAGE_TYPE_EMPTY, PAGE_SIZE/4);
-        memset(table + 256, 0, PAGE_SIZE/4);
-        clear_table(table + 512, _PAGE_TYPE_EMPTY, PAGE_SIZE/4);
-        memset(table + 768, 0, PAGE_SIZE/4);
-}
-
+#define FRAG_MASK       0x0f
 #else
 #define ALLOC_ORDER     2
-#define TABLES_PER_PAGE 2
-#define FRAG_MASK       3UL
-#define SECOND_HALVES   2UL
-
-void clear_table_pgstes(unsigned long *table)
-{
-        clear_table(table, _PAGE_TYPE_EMPTY, PAGE_SIZE/2);
-        memset(table + 256, 0, PAGE_SIZE/2);
-}
-
+#define FRAG_MASK       0x03
 #endif
 
 unsigned long VMALLOC_START = VMALLOC_END - VMALLOC_SIZE;
@@ -140,29 +58,6 @@ void crst_table_free(struct mm_struct *mm, unsigned long *table)
         free_pages((unsigned long) table, ALLOC_ORDER);
 }
 
-void crst_table_free_rcu(struct mm_struct *mm, unsigned long *table)
-{
-        struct rcu_table_freelist *batch;
-
-        preempt_disable();
-        if (atomic_read(&mm->mm_users) < 2 &&
-            cpumask_equal(mm_cpumask(mm), cpumask_of(smp_processor_id()))) {
-                crst_table_free(mm, table);
-                goto out;
-        }
-        batch = rcu_table_freelist_get(mm);
-        if (!batch) {
-                smp_call_function(smp_sync, NULL, 1);
-                crst_table_free(mm, table);
-                goto out;
-        }
-        batch->table[--batch->crst_index] = table;
-        if (batch->pgt_index >= batch->crst_index)
-                rcu_table_freelist_finish();
-out:
-        preempt_enable();
-}
-
 #ifdef CONFIG_64BIT
 int crst_table_upgrade(struct mm_struct *mm, unsigned long limit)
 {
@@ -238,124 +133,175 @@ void crst_table_downgrade(struct mm_struct *mm, unsigned long limit)
 }
 #endif
 
+static inline unsigned int atomic_xor_bits(atomic_t *v, unsigned int bits)
+{
+        unsigned int old, new;
+
+        do {
+                old = atomic_read(v);
+                new = old ^ bits;
+        } while (atomic_cmpxchg(v, old, new) != old);
+        return new;
+}
+
 /*
  * page table entry allocation/free routines.
  */
+#ifdef CONFIG_PGSTE
+static inline unsigned long *page_table_alloc_pgste(struct mm_struct *mm)
+{
+        struct page *page;
+        unsigned long *table;
+
+        page = alloc_page(GFP_KERNEL|__GFP_REPEAT);
+        if (!page)
+                return NULL;
+        pgtable_page_ctor(page);
+        atomic_set(&page->_mapcount, 3);
+        table = (unsigned long *) page_to_phys(page);
+        clear_table(table, _PAGE_TYPE_EMPTY, PAGE_SIZE/2);
+        clear_table(table + PTRS_PER_PTE, 0, PAGE_SIZE/2);
+        return table;
+}
+
+static inline void page_table_free_pgste(unsigned long *table)
+{
+        struct page *page;
+
+        page = pfn_to_page(__pa(table) >> PAGE_SHIFT);
+        pgtable_page_ctor(page);
+        atomic_set(&page->_mapcount, -1);
+        __free_page(page);
+}
+#endif
+
 unsigned long *page_table_alloc(struct mm_struct *mm)
 {
         struct page *page;
         unsigned long *table;
-        unsigned long bits;
+        unsigned int mask, bit;
 
-        bits = (mm->context.has_pgste) ? 3UL : 1UL;
+#ifdef CONFIG_PGSTE
+        if (mm_has_pgste(mm))
+                return page_table_alloc_pgste(mm);
+#endif
+        /* Allocate fragments of a 4K page as 1K/2K page table */
         spin_lock_bh(&mm->context.list_lock);
-        page = NULL;
+        mask = FRAG_MASK;
         if (!list_empty(&mm->context.pgtable_list)) {
                 page = list_first_entry(&mm->context.pgtable_list,
                                         struct page, lru);
-                if ((page->flags & FRAG_MASK) == ((1UL << TABLES_PER_PAGE) - 1))
-                        page = NULL;
+                table = (unsigned long *) page_to_phys(page);
+                mask = atomic_read(&page->_mapcount);
+                mask = mask | (mask >> 4);
         }
-        if (!page) {
+        if ((mask & FRAG_MASK) == FRAG_MASK) {
                 spin_unlock_bh(&mm->context.list_lock);
                 page = alloc_page(GFP_KERNEL|__GFP_REPEAT);
                 if (!page)
                         return NULL;
                 pgtable_page_ctor(page);
-                page->flags &= ~FRAG_MASK;
+                atomic_set(&page->_mapcount, 1);
                 table = (unsigned long *) page_to_phys(page);
-                if (mm->context.has_pgste)
-                        clear_table_pgstes(table);
-                else
-                        clear_table(table, _PAGE_TYPE_EMPTY, PAGE_SIZE);
+                clear_table(table, _PAGE_TYPE_EMPTY, PAGE_SIZE);
                 spin_lock_bh(&mm->context.list_lock);
                 list_add(&page->lru, &mm->context.pgtable_list);
+        } else {
+                for (bit = 1; mask & bit; bit <<= 1)
+                        table += PTRS_PER_PTE;
+                mask = atomic_xor_bits(&page->_mapcount, bit);
+                if ((mask & FRAG_MASK) == FRAG_MASK)
+                        list_del(&page->lru);
         }
-        table = (unsigned long *) page_to_phys(page);
-        while (page->flags & bits) {
-                table += 256;
-                bits <<= 1;
-        }
-        page->flags |= bits;
-        if ((page->flags & FRAG_MASK) == ((1UL << TABLES_PER_PAGE) - 1))
-                list_move_tail(&page->lru, &mm->context.pgtable_list);
         spin_unlock_bh(&mm->context.list_lock);
         return table;
 }
 
-static void __page_table_free(struct mm_struct *mm, unsigned long *table)
+void page_table_free(struct mm_struct *mm, unsigned long *table)
 {
         struct page *page;
-        unsigned long bits;
+        unsigned int bit, mask;
 
-        bits = ((unsigned long) table) & 15;
-        table = (unsigned long *)(((unsigned long) table) ^ bits);
+#ifdef CONFIG_PGSTE
+        if (mm_has_pgste(mm))
+                return page_table_free_pgste(table);
+#endif
+        /* Free 1K/2K page table fragment of a 4K page */
         page = pfn_to_page(__pa(table) >> PAGE_SHIFT);
-        page->flags ^= bits;
-        if (!(page->flags & FRAG_MASK)) {
+        bit = 1 << ((__pa(table) & ~PAGE_MASK)/(PTRS_PER_PTE*sizeof(pte_t)));
+        spin_lock_bh(&mm->context.list_lock);
+        if ((atomic_read(&page->_mapcount) & FRAG_MASK) != FRAG_MASK)
+                list_del(&page->lru);
+        mask = atomic_xor_bits(&page->_mapcount, bit);
+        if (mask & FRAG_MASK)
+                list_add(&page->lru, &mm->context.pgtable_list);
+        spin_unlock_bh(&mm->context.list_lock);
+        if (mask == 0) {
                 pgtable_page_dtor(page);
+                atomic_set(&page->_mapcount, -1);
                 __free_page(page);
         }
 }
 
-void page_table_free(struct mm_struct *mm, unsigned long *table)
+#ifdef CONFIG_HAVE_RCU_TABLE_FREE
+
+static void __page_table_free_rcu(void *table, unsigned bit)
 {
         struct page *page;
-        unsigned long bits;
 
-        bits = (mm->context.has_pgste) ? 3UL : 1UL;
-        bits <<= (__pa(table) & (PAGE_SIZE - 1)) / 256 / sizeof(unsigned long);
+#ifdef CONFIG_PGSTE
+        if (bit == FRAG_MASK)
+                return page_table_free_pgste(table);
+#endif
+        /* Free 1K/2K page table fragment of a 4K page */
         page = pfn_to_page(__pa(table) >> PAGE_SHIFT);
-        spin_lock_bh(&mm->context.list_lock);
-        page->flags ^= bits;
-        if (page->flags & FRAG_MASK) {
-                /* Page now has some free pgtable fragments. */
-                if (!list_empty(&page->lru))
-                        list_move(&page->lru, &mm->context.pgtable_list);
-                page = NULL;
-        } else
-                /* All fragments of the 4K page have been freed. */
-                list_del(&page->lru);
-        spin_unlock_bh(&mm->context.list_lock);
-        if (page) {
+        if (atomic_xor_bits(&page->_mapcount, bit) == 0) {
                 pgtable_page_dtor(page);
+                atomic_set(&page->_mapcount, -1);
                 __free_page(page);
         }
 }
 
-void page_table_free_rcu(struct mm_struct *mm, unsigned long *table)
+void page_table_free_rcu(struct mmu_gather *tlb, unsigned long *table)
 {
-        struct rcu_table_freelist *batch;
+        struct mm_struct *mm;
         struct page *page;
-        unsigned long bits;
+        unsigned int bit, mask;
 
-        preempt_disable();
-        if (atomic_read(&mm->mm_users) < 2 &&
-            cpumask_equal(mm_cpumask(mm), cpumask_of(smp_processor_id()))) {
-                page_table_free(mm, table);
-                goto out;
-        }
-        batch = rcu_table_freelist_get(mm);
-        if (!batch) {
-                smp_call_function(smp_sync, NULL, 1);
-                page_table_free(mm, table);
-                goto out;
+        mm = tlb->mm;
+#ifdef CONFIG_PGSTE
+        if (mm_has_pgste(mm)) {
+                table = (unsigned long *) (__pa(table) | FRAG_MASK);
+                tlb_remove_table(tlb, table);
+                return;
         }
-        bits = (mm->context.has_pgste) ? 3UL : 1UL;
-        bits <<= (__pa(table) & (PAGE_SIZE - 1)) / 256 / sizeof(unsigned long);
+#endif
+        bit = 1 << ((__pa(table) & ~PAGE_MASK) / (PTRS_PER_PTE*sizeof(pte_t)));
         page = pfn_to_page(__pa(table) >> PAGE_SHIFT);
         spin_lock_bh(&mm->context.list_lock);
-        /* Delayed freeing with rcu prevents reuse of pgtable fragments */
-        list_del_init(&page->lru);
+        if ((atomic_read(&page->_mapcount) & FRAG_MASK) != FRAG_MASK)
+                list_del(&page->lru);
+        mask = atomic_xor_bits(&page->_mapcount, bit | (bit << 4));
+        if (mask & FRAG_MASK)
+                list_add_tail(&page->lru, &mm->context.pgtable_list);
         spin_unlock_bh(&mm->context.list_lock);
-        table = (unsigned long *)(((unsigned long) table) | bits);
-        batch->table[batch->pgt_index++] = table;
-        if (batch->pgt_index >= batch->crst_index)
-                rcu_table_freelist_finish();
-out:
-        preempt_enable();
+        table = (unsigned long *) (__pa(table) | (bit << 4));
+        tlb_remove_table(tlb, table);
 }
 
+void __tlb_remove_table(void *_table)
+{
+        void *table = (void *)((unsigned long) _table & PAGE_MASK);
+        unsigned type = (unsigned long) _table & ~PAGE_MASK;
+
+        if (type)
+                __page_table_free_rcu(table, type);
+        else
+                free_pages((unsigned long) table, ALLOC_ORDER);
+}
+
+#endif
+
 /*
  * switch on pgstes for its userspace process (for kvm)
  */
@@ -369,7 +315,7 @@ int s390_enable_sie(void)
                 return -EINVAL;
 
         /* Do we have pgstes? if yes, we are done */
-        if (tsk->mm->context.has_pgste)
+        if (mm_has_pgste(tsk->mm))
                 return 0;
 
         /* lets check if we are allowed to replace the mm */