Re: [PATCH] s390/mm: Add missing ctor/dtor on page table upgrade

Gerald Schaefer
2025-01-23T16:51:34Z

On Thu, 23 Jan 2025 17:03:49 +0100
Alexander Gordeev <agordeev@linux.ibm.com> wrote:

> Commit 78966b550289 ("s390: pgtable: add statistics for PUD and P4D
> level page table") misses the call to pagetable_p4d_ctor() against
> a newly allocated P4D table in crst_table_upgrade();
>
> Commit 68c601de75d8 ("mm: introduce ctor/dtor at PGD level") misses
> the call to pagetable_pgd_ctor() against a newly allocated PGD and
> the call to pagetable_dtor() against a newly allocated P4D that is
> about to be freed on crst_table_upgrade() PGD upgrade fail path.
>
> The missed constructors and destructor break (at least) the page
> table accounting when a process memory space is upgraded.
>
> Reported-by: Heiko Carstens <hca@linux.ibm.com>
> Closes: https://lore.kernel.org/all/20250122074954.8685-A-hca@linux.ibm.com/
> Suggested-by: Heiko Carstens <hca@linux.ibm.com>
> Fixes: 78966b550289 ("s390: pgtable: add statistics for PUD and P4D level page table")
> Fixes: 68c601de75d8 ("mm: introduce ctor/dtor at PGD level")
> Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
> ---
> The patch is against:
>
> git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git next-20250123
> git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm mm-stable
> ---
> arch/s390/mm/pgalloc.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/arch/s390/mm/pgalloc.c b/arch/s390/mm/pgalloc.c
> index a4e761902093..d33f55b7ee98 100644
> --- a/arch/s390/mm/pgalloc.c
> +++ b/arch/s390/mm/pgalloc.c
> @@ -88,12 +88,14 @@ int crst_table_upgrade(struct mm_struct *mm, unsigned long end)
> if (unlikely(!p4d))
> goto err_p4d;
> crst_table_init(p4d, _REGION2_ENTRY_EMPTY);
> + pagetable_p4d_ctor(virt_to_ptdesc(p4d));
> }
> if (end > _REGION1_SIZE) {
> pgd = crst_table_alloc(mm);
> if (unlikely(!pgd))
> goto err_pgd;
> crst_table_init(pgd, _REGION1_ENTRY_EMPTY);
> + pagetable_pgd_ctor(virt_to_ptdesc(pgd));
> }
>
> spin_lock_bh(&mm->page_table_lock);
> @@ -130,6 +132,7 @@ int crst_table_upgrade(struct mm_struct *mm, unsigned long end)
> return 0;
>
> err_pgd:
> + pagetable_dtor(virt_to_ptdesc(p4d));
> crst_table_free(mm, p4d);
> err_p4d:
> return -ENOMEM;

Thanks, looks good, and nice catch.

Reviewed-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com>