On Tue, Oct 16, 2018 at 12:42 AM, Martin Schwidefsky <schwidefsky@xxxxxxxxxx> wrote:
In case a fork or a clone system fails in copy_process and the error
handling does the mmput() at the bad_fork_cleanup_mm label, the
following warning messages will appear on the console:
BUG: non-zero pgtables_bytes on freeing mm: 16384
The reason for that is the tricks we play with mm_inc_nr_puds() and
mm_inc_nr_pmds() in init_new_context().
A normal 64-bit process has 3 levels of page table, the p4d level and
the pud level are folded. On process termination the free_pud_range()
function in mm/memory.c will subtract 16KB from pgtable_bytes with a
mm_dec_nr_puds() call, but there actually is not really a pud table.
One issue with this is the fact that pgtable_bytes is usually off
by a few kilobytes, but the more severe problem is that for a failed
fork or clone the free_pgtables() function is not called. In this case
there is no mm_dec_nr_puds() or mm_dec_nr_pmds() that go together with
the mm_inc_nr_puds() and mm_inc_nr_pmds in init_new_context().
The pgtable_bytes will be off by 16384 or 32768 bytes and we get the
BUG message. The message itself is purely cosmetic, but annoying.
To fix this override the mm_pmd_folded, mm_pud_folded and mm_p4d_folded
function to check for the true size of the address space.
I can confirm that it works to the problem, the warning message is gone after applying this patch on s390x. And I also done ltp syscalls/cve test for the patch set on x86_64 arch, there has no new regression.
Reported-by: Li Wang <liwang@xxxxxxxxxx>
Signed-off-by: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
---
arch/s390/include/asm/mmu_context.h | 5 -----
arch/s390/include/asm/pgalloc.h | 6 +++---
arch/s390/include/asm/pgtable.h | 18 ++++++++++++++++++
arch/s390/include/asm/tlb.h | 6 +++---
4 files changed, 24 insertions(+), 11 deletions(-)
diff --git a/arch/s390/include/asm/mmu_context.h b/arch/s390/include/asm/mmu_co ntext.h
index 0717ee76885d..f1ab9420ccfb 100644
--- a/arch/s390/include/asm/mmu_context.h
+++ b/arch/s390/include/asm/mmu_context.h
@@ -45,8 +45,6 @@ static inline int init_new_context(struct task_struct *tsk,
mm->context.asce_limit = STACK_TOP_MAX;
mm->context.asce = __pa(mm->pgd) | _ASCE_TABLE_LENGTH |
_ASCE_USER_BITS | _ASCE_TYPE_REGION3;
- /* pgd_alloc() did not account this pud */
- mm_inc_nr_puds(mm);
break;
case -PAGE_SIZE:
/* forked 5-level task, set new asce with new_mm->pgd */
@@ -62,9 +60,6 @@ static inline int init_new_context(struct task_struct *tsk,
/* forked 2-level compat task, set new asce with new mm->pgd */
mm->context.asce = __pa(mm->pgd) | _ASCE_TABLE_LENGTH |
_ASCE_USER_BITS | _ASCE_TYPE_SEGMENT;
- /* pgd_alloc() did not account this pmd */
- mm_inc_nr_pmds(mm);
- mm_inc_nr_puds(mm);
}
crst_table_init((unsigned long *) mm->pgd, pgd_entry_type(mm));
return 0;
diff --git a/arch/s390/include/asm/pgalloc.h b/arch/s390/include/asm/pgallo c.h
index f0f9bcf94c03..5ee733720a57 100644
--- a/arch/s390/include/asm/pgalloc.h
+++ b/arch/s390/include/asm/pgalloc.h
@@ -36,11 +36,11 @@ static inline void crst_table_init(unsigned long *crst, unsigned long entry)
static inline unsigned long pgd_entry_type(struct mm_struct *mm)
{
- if (mm->context.asce_limit <= _REGION3_SIZE)
+ if (mm_pmd_folded(mm))
return _SEGMENT_ENTRY_EMPTY;
- if (mm->context.asce_limit <= _REGION2_SIZE)
+ if (mm_pud_folded(mm))
return _REGION3_ENTRY_EMPTY;
- if (mm->context.asce_limit <= _REGION1_SIZE)
+ if (mm_p4d_folded(mm))
return _REGION2_ENTRY_EMPTY;
return _REGION1_ENTRY_EMPTY;
}
diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtabl e.h
index 0e7cb0dc9c33..de05466ce50c 100644
--- a/arch/s390/include/asm/pgtable.h
+++ b/arch/s390/include/asm/pgtable.h
@@ -485,6 +485,24 @@ static inline int is_module_addr(void *addr)
_REGION_ENTRY_PROTECT | \
_REGION_ENTRY_NOEXEC)
+static inline bool mm_p4d_folded(struct mm_struct *mm)
+{
+ return mm->context.asce_limit <= _REGION1_SIZE;
+}
+#define mm_p4d_folded(mm) mm_p4d_folded(mm)
+
+static inline bool mm_pud_folded(struct mm_struct *mm)
+{
+ return mm->context.asce_limit <= _REGION2_SIZE;
+}
+#define mm_pud_folded(mm) mm_pud_folded(mm)
+
+static inline bool mm_pmd_folded(struct mm_struct *mm)
+{
+ return mm->context.asce_limit <= _REGION3_SIZE;
+}
+#define mm_pmd_folded(mm) mm_pmd_folded(mm)
+
static inline int mm_has_pgste(struct mm_struct *mm)
{
#ifdef CONFIG_PGSTE
diff --git a/arch/s390/include/asm/tlb.h b/arch/s390/include/asm/tlb.h
index 457b7ba0fbb6..b31c779cf581 100644
--- a/arch/s390/include/asm/tlb.h
+++ b/arch/s390/include/asm/tlb.h
@@ -136,7 +136,7 @@ static inline void pte_free_tlb(struct mmu_gather *tlb, pgtable_t pte,
static inline void pmd_free_tlb(struct mmu_gather *tlb, pmd_t *pmd,
unsigned long address)
{
- if (tlb->mm->context.asce_limit <= _REGION3_SIZE)
+ if (mm_pmd_folded(tlb->mm))
return;
pgtable_pmd_page_dtor(virt_to_page(pmd));
tlb_remove_table(tlb, pmd);
@@ -152,7 +152,7 @@ static inline void pmd_free_tlb(struct mmu_gather *tlb, pmd_t *pmd,
static inline void p4d_free_tlb(struct mmu_gather *tlb, p4d_t *p4d,
unsigned long address)
{
- if (tlb->mm->context.asce_limit <= _REGION1_SIZE)
+ if (mm_p4d_folded(tlb->mm))
return;
tlb_remove_table(tlb, p4d);
}
@@ -167,7 +167,7 @@ static inline void p4d_free_tlb(struct mmu_gather *tlb, p4d_t *p4d,
static inline void pud_free_tlb(struct mmu_gather *tlb, pud_t *pud,
unsigned long address)
{
- if (tlb->mm->context.asce_limit <= _REGION2_SIZE)
+ if (mm_pud_folded(tlb->mm))
return;
tlb_remove_table(tlb, pud);
}
--
2.16.4
Regards,
Li Wang
