Re: [PATCH v2] mm/hugetlb: fix hugetlb vs. core-mm PT locking

James Houghton
2024-07-30T20:44:15Z

On Tue, Jul 30, 2024 at 1:03 PM David Hildenbrand <david@redhat.com> wrote:
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index b100df8cb5857..1b1f40ff00b7d 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2926,6 +2926,12 @@ static inline spinlock_t *pte_lockptr(struct mm_struct *mm, pmd_t *pmd)
> return ptlock_ptr(page_ptdesc(pmd_page(*pmd)));
> }
>
> +static inline spinlock_t *ptep_lockptr(struct mm_struct *mm, pte_t *pte)
> +{
> + BUILD_BUG_ON(IS_ENABLED(CONFIG_HIGHPTE));
> + return ptlock_ptr(virt_to_ptdesc(pte));

Hi David,

Small question: ptep_lockptr() does not handle the case where the size
of the PTE table is larger than PAGE_SIZE, but pmd_lockptr() does.
IIUC, for pte_lockptr() and ptep_lockptr() to return the same result
in this case, ptep_lockptr() should be doing the masking that
pmd_lockptr() is doing. Are you sure that you don't need to be doing
it? (Or maybe I am misunderstanding something.)

Thanks for the fix!

> +}
> +
> static inline bool ptlock_init(struct ptdesc *ptdesc)
> {
> /*
> @@ -2950,6 +2956,10 @@ static inline spinlock_t *pte_lockptr(struct mm_struct *mm, pmd_t *pmd)
> {
> return &mm->page_table_lock;
> }
> +static inline spinlock_t *ptep_lockptr(struct mm_struct *mm, pte_t *pte)
> +{
> + return &mm->page_table_lock;
> +}
> static inline void ptlock_cache_init(void) {}
> static inline bool ptlock_init(struct ptdesc *ptdesc) { return true; }
> static inline void ptlock_free(struct ptdesc *ptdesc) {}
> --
> 2.45.2
>
>