lkml.org 
[lkml]   [2008]   [Oct]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[patch 4/5] pgtables: Fix race in enable_sie vs. page table ops
From: Christian Borntraeger <borntraeger@de.ibm.com>

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>
---

arch/s390/include/asm/mmu.h | 3 ++-
arch/s390/include/asm/mmu_context.h | 19 ++++++++++++++++---
arch/s390/include/asm/pgtable.h | 8 ++++----
arch/s390/mm/pgtable.c | 16 ++++++++--------
4 files changed, 30 insertions(+), 16 deletions(-)

Index: quilt-2.6/arch/s390/include/asm/mmu_context.h
===================================================================
--- quilt-2.6.orig/arch/s390/include/asm/mmu_context.h
+++ quilt-2.6/arch/s390/include/asm/mmu_context.h
@@ -20,12 +20,25 @@ static inline int init_new_context(struc
#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));
Index: quilt-2.6/arch/s390/include/asm/mmu.h
===================================================================
--- quilt-2.6.orig/arch/s390/include/asm/mmu.h
+++ quilt-2.6/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
Index: quilt-2.6/arch/s390/include/asm/pgtable.h
===================================================================
--- quilt-2.6.orig/arch/s390/include/asm/pgtable.h
+++ quilt-2.6/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_clea
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_yo
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
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);
Index: quilt-2.6/arch/s390/mm/pgtable.c
===================================================================
--- quilt-2.6.orig/arch/s390/mm/pgtable.c
+++ quilt-2.6/arch/s390/mm/pgtable.c
@@ -169,7 +169,7 @@ unsigned long *page_table_alloc(struct m
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 m
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 *m
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) {
--
blue skies,
Martin.

"Reality continues to ruin my life." - Calvin.



\
 
 \ /
  Last update: 2008-10-15 19:53    [W:0.041 / U:3.388 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site