[S390] fix tlb flushing for page table pages

Git commit 36409f6353fc2d7b6516e631415f938eadd92ffa "use generic RCU
page-table freeing code" introduced a tlb flushing bug. Partially revert
the above git commit and go back to s390 specific page table flush code.

For s390 the TLB can contain three types of entries, "normal" TLB
page-table entries, TLB combined region-and-segment-table (CRST) entries
and real-space entries. Linux does not use real-space entries which
leaves normal TLB entries and CRST entries. The CRST entries are
intermediate steps in the page-table translation called translation paths.
For example a 4K page access in a three-level page table setup will
create two CRST TLB entries and one page-table TLB entry. The advantage
of that approach is that a page access next to the previous one can reuse
the CRST entries and needs just a single read from memory to create the
page-table TLB entry. The disadvantage is that the TLB flushing rules are
more complicated, before any page-table may be freed the TLB needs to be
flushed.

In short: the generic RCU page-table freeing code is incorrect for the
CRST entries, in particular the check for mm_users < 2 is troublesome.

This is applicable to 3.0+ kernels.

Cc: <stable@vger.kernel.org>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

4 files changed, 61 insertions, 28 deletions

diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index 2b7c0fbe578e..9015060919a0 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -90,7 +90,6 @@ config S390
         select HAVE_KERNEL_XZ
         select HAVE_ARCH_MUTEX_CPU_RELAX
         select HAVE_ARCH_JUMP_LABEL if !MARCH_G5
-        select HAVE_RCU_TABLE_FREE if SMP
         select ARCH_SAVE_PAGE_KEYS if HIBERNATION
         select HAVE_MEMBLOCK
         select HAVE_MEMBLOCK_NODE_MAP
diff --git a/arch/s390/include/asm/pgalloc.h b/arch/s390/include/asm/pgalloc.h
index 8eef9b5b3cf4..78e3041919de 100644
--- a/arch/s390/include/asm/pgalloc.h
+++ b/arch/s390/include/asm/pgalloc.h
@@ -22,10 +22,7 @@ void crst_table_free(struct mm_struct *, unsigned long *);
 
 unsigned long *page_table_alloc(struct mm_struct *, unsigned long);
 void page_table_free(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 c687a2c83462..775a5eea8f9e 100644
--- a/arch/s390/include/asm/tlb.h
+++ b/arch/s390/include/asm/tlb.h
@@ -30,14 +30,10 @@
 
 struct mmu_gather {
         struct mm_struct *mm;
-#ifdef CONFIG_HAVE_RCU_TABLE_FREE
         struct mmu_table_batch *batch;
-#endif
         unsigned int fullmm;
-        unsigned int need_flush;
 };
 
-#ifdef CONFIG_HAVE_RCU_TABLE_FREE
 struct mmu_table_batch {
         struct rcu_head         rcu;
         unsigned int            nr;
@@ -49,7 +45,6 @@ struct mmu_table_batch {
 
 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,
@@ -57,29 +52,20 @@ static inline void tlb_gather_mmu(struct mmu_gather *tlb,
 {
         tlb->mm = mm;
         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);
 }
 
 static inline void tlb_flush_mmu(struct mmu_gather *tlb)
 {
-        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);
+        tlb_table_flush(tlb);
 }
 
 /*
@@ -105,10 +91,8 @@ 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)
 {
-#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);
 }
 
@@ -125,10 +109,8 @@ static inline void pmd_free_tlb(struct mmu_gather *tlb, pmd_t *pmd,
 #ifdef __s390x__
         if (tlb->mm->context.asce_limit <= (1UL << 31))
                 return;
-#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
 }
@@ -146,10 +128,8 @@ static inline void pud_free_tlb(struct mmu_gather *tlb, pud_t *pud,
 #ifdef __s390x__
         if (tlb->mm->context.asce_limit <= (1UL << 42))
                 return;
-#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 373adf69b01c..6e765bf00670 100644
--- a/arch/s390/mm/pgtable.c
+++ b/arch/s390/mm/pgtable.c
@@ -678,8 +678,6 @@ 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;
@@ -733,7 +731,66 @@ void __tlb_remove_table(void *_table)
                 free_pages((unsigned long) table, ALLOC_ORDER);
 }
 
-#endif
+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) {
+                __tlb_flush_mm(tlb->mm);
+                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;
+
+        if (*batch == NULL) {
+                *batch = (struct mmu_table_batch *)
+                        __get_free_page(GFP_NOWAIT | __GFP_NOWARN);
+                if (*batch == NULL) {
+                        __tlb_flush_mm(tlb->mm);
+                        tlb_remove_table_one(table);
+                        return;
+                }
+                (*batch)->nr = 0;
+        }
+        (*batch)->tables[(*batch)->nr++] = table;
+        if ((*batch)->nr == MAX_TABLE_BATCH)
+                tlb_table_flush(tlb);
+}
 
 /*
  * switch on pgstes for its userspace process (for kvm)