Re: s390: runtime warning about pgtables_bytes

From: Joe Lawrence
Date: Wed Oct 31 2018 - 15:58:03 EST

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On Fri, Oct 12, 2018 at 05:08:33PM +0200, Martin Schwidefsky wrote:
> On Thu, 11 Oct 2018 15:02:11 +0200
> Martin Schwidefsky <schwidefsky@xxxxxxxxxx> wrote:
>
> > On Thu, 11 Oct 2018 18:04:12 +0800
> > Li Wang <liwang@xxxxxxxxxx> wrote:
> >
> > > When running s390 system with LTP/cve-2017-17052.c[1], the following BUG is
> > > came out repeatedly.
> > > I remember this warning start from kernel-4.16.0 and now it still exist in
> > > kernel-4.19-rc7.
> > > Can anyone take a look?
> > >
> > > [ 2678.991496] BUG: non-zero pgtables_bytes on freeing mm: 16384
> > > [ 2679.001543] BUG: non-zero pgtables_bytes on freeing mm: 16384
> > > [ 2679.002453] BUG: non-zero pgtables_bytes on freeing mm: 16384
> > > [ 2679.003256] BUG: non-zero pgtables_bytes on freeing mm: 16384
> > > [ 2679.013689] BUG: non-zero pgtables_bytes on freeing mm: 16384
> > > [ 2679.024647] BUG: non-zero pgtables_bytes on freeing mm: 16384
> > > [ 2679.064408] BUG: non-zero pgtables_bytes on freeing mm: 16384
> > > [ 2679.133963] BUG: non-zero pgtables_bytes on freeing mm: 16384
> > >
> > > [1]:
> > > https://github.com/linux-test-project/ltp/blob/master/testcases/cve/cve-2017-17052.c
> >
> > Confirmed, I see this bug with cvs-2017-17052 on my LPAR as well.
> > I'll look into it.
>
> Ok, I think I understand the problem now. This is the patch I am testing
> right now. It seems to fix the issue, but I had to change common mm
> code for it.
> --
> >From 9e3bc2e96930206ef1ece377e45224c51aca1799 Mon Sep 17 00:00:00 2001
> From: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
> Date: Fri, 12 Oct 2018 16:32:29 +0200
> Subject: [RFC][PATCH] s390/mm: fix mis-accounting of pgtable_bytes
>
> 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.
> The s390 version of pud_free_tlb() recognized this an does nothing,
> the region-3 table will be freed with the pgd_free() call later on.
> But the mm_dec_nr_puds() is done unconditionally, to counter act this
> the init_new_context() function has an extra mm_inc_nr_puds() call.
>
> Now with a failed fork or clone the free_pgtables() function is not
> called, there is no mm_dec_nr_puds() but the mm_inc_nr_puds() has
> been done which leads to the incorrect pgtable_bytes of 16384.
> Nothing is broken by this, but the warning is annoying.
>
> To get rid of the warning drop the mm_inc_nr_pmds() & mm_inc_nr_puds()
> calls from init_new_context(), introduce the mm_pmd_folded(),
> pmd_pud_folded() and pmd_p4d_folded() helper, and add if-statements
> to the functions mm_[inc|dec]_nr_[pmds|puds].
>
> 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 ++---
> include/linux/mm.h | 44 ++++++++++++++++++++++++++++++++-----
> 5 files changed, 62 insertions(+), 17 deletions(-)
>
> diff --git a/arch/s390/include/asm/mmu_context.h b/arch/s390/include/asm/mmu_context.h
> index dbd689d556ce..ccbb53e22024 100644
> --- a/arch/s390/include/asm/mmu_context.h
> +++ b/arch/s390/include/asm/mmu_context.h
> @@ -46,8 +46,6 @@ 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 */
> @@ -63,9 +61,6 @@ 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/pgalloc.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/pgtable.h
> index 411d435e7a7d..063732414dfb 100644
> --- a/arch/s390/include/asm/pgtable.h
> +++ b/arch/s390/include/asm/pgtable.h
> @@ -493,6 +493,24 @@ 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);
> }
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 0416a7204be3..1e4a045f19ec 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -105,6 +105,34 @@ extern int mmap_rnd_compat_bits __read_mostly;
> #define mm_zero_struct_page(pp) ((void)memset((pp), 0, sizeof(struct page)))
> #endif
>
> +/*
> + * On some architectures it depends on the mm if the p4d/pud or pmd
> + * layer of the page table hierarchy is folded or not.
> + */
> +#ifndef mm_p4d_folded
> +#define mm_p4d_folded(mm) mm_p4d_folded(mm)
> +static inline bool mm_p4d_folded(struct mm_struct *mm)
> +{
> + return __is_defined(__PAGETABLE_P4D_FOLDED);
> +}
> +#endif
> +
> +#ifndef mm_pud_folded
> +#define mm_pud_folded(mm) mm_pud_folded(mm)
> +static inline bool mm_pud_folded(struct mm_struct *mm)
> +{
> + return __is_defined(__PAGETABLE_PUD_FOLDED);
> +}
> +#endif
> +
> +#ifndef mm_pmd_folded
> +#define mm_pmd_folded(mm) mm_pmd_folded(mm)
> +static inline bool mm_pmd_folded(struct mm_struct *mm)
> +{
> + return __is_defined(__PAGETABLE_PMD_FOLDED);
> +}
> +#endif
> +
> /*
> * Default maximum number of active map areas, this limits the number of vmas
> * per mm struct. Users can overwrite this number by sysctl but there is a
> @@ -1710,7 +1738,7 @@ static inline int __p4d_alloc(struct mm_struct *mm, pgd_t *pgd,
> int __p4d_alloc(struct mm_struct *mm, pgd_t *pgd, unsigned long address);
> #endif
>
> -#if defined(__PAGETABLE_PUD_FOLDED) || !defined(CONFIG_MMU)
> +#if !defined(CONFIG_MMU)
> static inline int __pud_alloc(struct mm_struct *mm, p4d_t *p4d,
> unsigned long address)
> {
> @@ -1724,16 +1752,18 @@ int __pud_alloc(struct mm_struct *mm, p4d_t *p4d, unsigned long address);
>
> static inline void mm_inc_nr_puds(struct mm_struct *mm)
> {
> - atomic_long_add(PTRS_PER_PUD * sizeof(pud_t), &mm->pgtables_bytes);
> + if (!mm_pud_folded(mm))
> + atomic_long_add(PTRS_PER_PUD * sizeof(pud_t), &mm->pgtables_bytes);
> }
>
> static inline void mm_dec_nr_puds(struct mm_struct *mm)
> {
> - atomic_long_sub(PTRS_PER_PUD * sizeof(pud_t), &mm->pgtables_bytes);
> + if (!mm_pud_folded(mm))
> + atomic_long_sub(PTRS_PER_PUD * sizeof(pud_t), &mm->pgtables_bytes);
> }
> #endif
>
> -#if defined(__PAGETABLE_PMD_FOLDED) || !defined(CONFIG_MMU)
> +#if !defined(CONFIG_MMU)
> static inline int __pmd_alloc(struct mm_struct *mm, pud_t *pud,
> unsigned long address)
> {
> @@ -1748,12 +1778,14 @@ int __pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long address);
>
> static inline void mm_inc_nr_pmds(struct mm_struct *mm)
> {
> - atomic_long_add(PTRS_PER_PMD * sizeof(pmd_t), &mm->pgtables_bytes);
> + if (!mm_pmd_folded(mm))
> + atomic_long_add(PTRS_PER_PMD * sizeof(pmd_t), &mm->pgtables_bytes);
> }
>
> static inline void mm_dec_nr_pmds(struct mm_struct *mm)
> {
> - atomic_long_sub(PTRS_PER_PMD * sizeof(pmd_t), &mm->pgtables_bytes);
> + if (!mm_pmd_folded(mm))
> + atomic_long_sub(PTRS_PER_PMD * sizeof(pmd_t), &mm->pgtables_bytes);
> }
> #endif
>
> --
> 2.16.4
>
>
> --

Hi Martin,

We've seen these "non-zero pgtable byte" complaints as well and I found
this thread + test patch. Looks good after applying and running the LTP
cve-2017-17052 test over here.

Did this need further testing and/or review? I didn't see it in the
kernel/git/s390/linux.git tree so I thought I would ask.

Thanks,

-- Joe

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