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

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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>
This commit is contained in:
Christian Borntraeger
2008-10-28 11:10:15 +01:00
committed by Martin Schwidefsky
parent 2c78091405
commit 250cf776f7
4 changed files with 30 additions and 16 deletions
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19
arch/s390/include/asm/mmu_context.h
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@@ -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));