[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>
diff --git a/arch/s390/include/asm/mmu_context.h b/arch/s390/include/asm/mmu_context.h
index 4c2fbf4..28ec870 100644
--- a/arch/s390/include/asm/mmu_context.h
+++ b/arch/s390/include/asm/mmu_context.h
@@ -20,12 +20,25 @@
#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));