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

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Message-ID: <CADrL8HXRCNFzmg67p=j0_0Y_NAFo5rUDmvnr40F5HGAsQMvbnw@mail.gmail.com>
Date: Tue, 30 Jul 2024 13:43:35 -0700
From: James Houghton <jthoughton@...gle.com>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, stable@...r.kernel.org, 
	Peter Xu <peterx@...hat.com>, Oscar Salvador <osalvador@...e.de>, 
	Muchun Song <muchun.song@...ux.dev>, Baolin Wang <baolin.wang@...ux.alibaba.com>
Subject: Re: [PATCH v2] mm/hugetlb: fix hugetlb vs. core-mm PT locking

On Tue, Jul 30, 2024 at 1:03 PM David Hildenbrand <david@...hat.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
>
>