[S390] pgtables: Fix race in enable_sie vs. page table ops

The current enable_sie code sets the mm->context.pgstes bit to tell
dup_mm that the new mm should have extended page tables. This bit is also
used by the s390 specific page table primitives to decide about the page
table layout - which means context.pgstes has two meanings. This can cause
any kind of bugs. For example  - e.g. shrink_zone can call
ptep_clear_flush_young while enable_sie is running. ptep_clear_flush_young
will test for context.pgstes. Since enable_sie changed that value of the old
struct mm without changing the page table layout ptep_clear_flush_young will
do the wrong thing.
The solution is to split pgstes into two bits
- one for the allocation
- one for the current state

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

4 files changed, 30 insertions, 16 deletions

diff --git a/arch/s390/include/asm/mmu.h b/arch/s390/include/asm/mmu.h
index 5dd5e7b3476f..d2b4ff831477 100644
--- a/arch/s390/include/asm/mmu.h
+++ b/arch/s390/include/asm/mmu.h
@@ -7,7 +7,8 @@ typedef struct {
         unsigned long asce_bits;
         unsigned long asce_limit;
         int noexec;
-        int pgstes;
+        int has_pgste;   /* The mmu context has extended page tables */
+        int alloc_pgste; /* cloned contexts will have extended page tables */
 } mm_context_t;
 
 #endif
diff --git a/arch/s390/include/asm/mmu_context.h b/arch/s390/include/asm/mmu_context.h
index 4c2fbf48c9c4..28ec870655af 100644
--- a/arch/s390/include/asm/mmu_context.h
+++ b/arch/s390/include/asm/mmu_context.h
@@ -20,12 +20,25 @@ static inline int init_new_context(struct task_struct *tsk,
 #ifdef CONFIG_64BIT
         mm->context.asce_bits |= _ASCE_TYPE_REGION3;
 #endif
-        if (current->mm->context.pgstes) {
+        if (current->mm->context.alloc_pgste) {
+                /*
+                 * alloc_pgste indicates, that any NEW context will be created
+                 * with extended page tables. The old context is unchanged. The
+                 * page table allocation and the page table operations will
+                 * look at has_pgste to distinguish normal and extended page
+                 * tables. The only way to create extended page tables is to
+                 * set alloc_pgste and then create a new context (e.g. dup_mm).
+                 * The page table allocation is called after init_new_context
+                 * and if has_pgste is set, it will create extended page
+                 * tables.
+                 */
                 mm->context.noexec = 0;
-                mm->context.pgstes = 1;
+                mm->context.has_pgste = 1;
+                mm->context.alloc_pgste = 1;
         } else {
                 mm->context.noexec = s390_noexec;
-                mm->context.pgstes = 0;
+                mm->context.has_pgste = 0;
+                mm->context.alloc_pgste = 0;
         }
         mm->context.asce_limit = STACK_TOP_MAX;
         crst_table_init((unsigned long *) mm->pgd, pgd_entry_type(mm));
diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
index 1a928f84afd6..7fc76133b3e4 100644
--- a/arch/s390/include/asm/pgtable.h
+++ b/arch/s390/include/asm/pgtable.h
@@ -679,7 +679,7 @@ static inline void pmd_clear(pmd_t *pmd)
 
 static inline void pte_clear(struct mm_struct *mm, unsigned long addr, pte_t *ptep)
 {
-        if (mm->context.pgstes)
+        if (mm->context.has_pgste)
                 ptep_rcp_copy(ptep);
         pte_val(*ptep) = _PAGE_TYPE_EMPTY;
         if (mm->context.noexec)
@@ -763,7 +763,7 @@ static inline int kvm_s390_test_and_clear_page_dirty(struct mm_struct *mm,
         struct page *page;
         unsigned int skey;
 
-        if (!mm->context.pgstes)
+        if (!mm->context.has_pgste)
                 return -EINVAL;
         rcp_lock(ptep);
         pgste = (unsigned long *) (ptep + PTRS_PER_PTE);
@@ -794,7 +794,7 @@ static inline int ptep_test_and_clear_young(struct vm_area_struct *vma,
         int young;
         unsigned long *pgste;
 
-        if (!vma->vm_mm->context.pgstes)
+        if (!vma->vm_mm->context.has_pgste)
                 return 0;
         physpage = pte_val(*ptep) & PAGE_MASK;
         pgste = (unsigned long *) (ptep + PTRS_PER_PTE);
@@ -844,7 +844,7 @@ static inline void __ptep_ipte(unsigned long address, pte_t *ptep)
 static inline void ptep_invalidate(struct mm_struct *mm,
                                    unsigned long address, pte_t *ptep)
 {
-        if (mm->context.pgstes) {
+        if (mm->context.has_pgste) {
                 rcp_lock(ptep);
                 __ptep_ipte(address, ptep);
                 ptep_rcp_copy(ptep);
diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c
index 3d98ba82ea67..ef3635b52fc0 100644
--- a/arch/s390/mm/pgtable.c
+++ b/arch/s390/mm/pgtable.c
@@ -169,7 +169,7 @@ unsigned long *page_table_alloc(struct mm_struct *mm)
         unsigned long *table;
         unsigned long bits;
 
-        bits = (mm->context.noexec || mm->context.pgstes) ? 3UL : 1UL;
+        bits = (mm->context.noexec || mm->context.has_pgste) ? 3UL : 1UL;
         spin_lock(&mm->page_table_lock);
         page = NULL;
         if (!list_empty(&mm->context.pgtable_list)) {
@@ -186,7 +186,7 @@ unsigned long *page_table_alloc(struct mm_struct *mm)
                 pgtable_page_ctor(page);
                 page->flags &= ~FRAG_MASK;
                 table = (unsigned long *) page_to_phys(page);
-                if (mm->context.pgstes)
+                if (mm->context.has_pgste)
                         clear_table_pgstes(table);
                 else
                         clear_table(table, _PAGE_TYPE_EMPTY, PAGE_SIZE);
@@ -210,7 +210,7 @@ void page_table_free(struct mm_struct *mm, unsigned long *table)
         struct page *page;
         unsigned long bits;
 
-        bits = (mm->context.noexec || mm->context.pgstes) ? 3UL : 1UL;
+        bits = (mm->context.noexec || mm->context.has_pgste) ? 3UL : 1UL;
         bits <<= (__pa(table) & (PAGE_SIZE - 1)) / 256 / sizeof(unsigned long);
         page = pfn_to_page(__pa(table) >> PAGE_SHIFT);
         spin_lock(&mm->page_table_lock);
@@ -257,7 +257,7 @@ int s390_enable_sie(void)
         struct mm_struct *mm, *old_mm;
 
         /* Do we have pgstes? if yes, we are done */
-        if (tsk->mm->context.pgstes)
+        if (tsk->mm->context.has_pgste)
                 return 0;
 
         /* lets check if we are allowed to replace the mm */
@@ -269,14 +269,14 @@ int s390_enable_sie(void)
         }
         task_unlock(tsk);
 
-        /* we copy the mm with pgstes enabled */
-        tsk->mm->context.pgstes = 1;
+        /* we copy the mm and let dup_mm create the page tables with_pgstes */
+        tsk->mm->context.alloc_pgste = 1;
         mm = dup_mm(tsk);
-        tsk->mm->context.pgstes = 0;
+        tsk->mm->context.alloc_pgste = 0;
         if (!mm)
                 return -ENOMEM;
 
-        /* Now lets check again if somebody attached ptrace etc */
+        /* Now lets check again if something happened */
         task_lock(tsk);
         if (!tsk->mm || atomic_read(&tsk->mm->mm_users) > 1 ||
             tsk->mm != tsk->active_mm || tsk->mm->ioctx_list) {