s390/mm: fix mis-accounting of pgtable_bytes

BugLink: https://bugs.launchpad.net/bugs/1836968
[ Upstream commit e12e4044aede97974f2222eb7f0ed726a5179a32 ]

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.

Reported-by: Li Wang <liwang@redhat.com>
Tested-by: Li Wang <liwang@redhat.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/arch/s390/include/asm/mmu_context.h b/arch/s390/include/asm/mmu_context.h
index 65154eaa3714a4e9182cb87654e7b896e7be3e2f..c2550432ecf742c37aa6958d3cb0b8ff9d8a4e3f 100644 (file)
--- a/arch/s390/include/asm/mmu_context.h
+++ b/arch/s390/include/asm/mmu_context.h
@@ -44,8 +44,6 @@ 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 */
@@ -61,8 +59,6 @@ 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);
        }
        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/pgalloc.h
index c7b4333d1de0aafe38ecccf606dde62053404be0..67ddb0e4540c27998c5c3cf7c728f24f7865b7fe 100644 (file)
--- 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/pgtable.h
index 0a6b0286c32e9e0a7283d9cfb66dc357fe2e36fa..fcf5fc0e584fad931ce005580d2abac2f977b7ad 100644 (file)
--- a/arch/s390/include/asm/pgtable.h
+++ b/arch/s390/include/asm/pgtable.h
@@ -484,6 +484,24 @@ 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 457b7ba0fbb66de24fd82219e18a51ad2663221f..b31c779cf58176ad3bf91ee816053cbcf40b3476 100644 (file)
--- 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);
 }

diff --git a/arch/s390/mm/pgalloc.c b/arch/s390/mm/pgalloc.c
index 2462a0ca916dfe4b19b98d60b5ef88166f3e908a..c4d7b64fa3fc57df2b18b006aa64b53d60c84e1b 100644 (file)
--- a/arch/s390/mm/pgalloc.c
+++ b/arch/s390/mm/pgalloc.c
@@ -100,6 +100,7 @@ int crst_table_upgrade(struct mm_struct *mm, unsigned long end)
                        mm->context.asce_limit = _REGION1_SIZE;
                        mm->context.asce = __pa(mm->pgd) | _ASCE_TABLE_LENGTH |
                                _ASCE_USER_BITS | _ASCE_TYPE_REGION2;
+                       mm_inc_nr_puds(mm);
                } else {
                        crst_table_init(table, _REGION1_ENTRY_EMPTY);
                        pgd_populate(mm, (pgd_t *) table, (p4d_t *) pgd);