[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>

1 files changed, 8 insertions, 8 deletions

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) {