Messages in this thread | | | Subject | Re: [PATCH 4/6] mm: hugetlb_vmemmap: add missing smp_wmb() before set_pte_at() | From | Miaohe Lin <> | Date | Wed, 17 Aug 2022 16:41:40 +0800 |
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On 2022/8/17 10:53, Muchun Song wrote: > > >> On Aug 16, 2022, at 21:05, Miaohe Lin <linmiaohe@huawei.com> wrote: >> >> The memory barrier smp_wmb() is needed to make sure that preceding stores >> to the page contents become visible before the below set_pte_at() write. > > I’m not sure if you are right. I think it is set_pte_at()’s responsibility.
Maybe not. There're many call sites do the similar things:
hugetlb_mcopy_atomic_pte __do_huge_pmd_anonymous_page collapse_huge_page do_anonymous_page migrate_vma_insert_page mcopy_atomic_pte
Take do_anonymous_page as an example:
/* * The memory barrier inside __SetPageUptodate makes sure that * preceding stores to the page contents become visible before * the set_pte_at() write. */ __SetPageUptodate(page);
So I think a memory barrier is needed before the set_pte_at() write. Or am I miss something?
Thanks, Miaohe Lin
> Take arm64 (since it is a Relaxed Memory Order model) as an example (the > following code snippet is set_pte()), I see a barrier guarantee. So I am > curious what issues you are facing. So I want to know the basis for you to > do this change. > > static inline void set_pte(pte_t *ptep, pte_t pte) > { > *ptep = pte; > > /* > * Only if the new pte is valid and kernel, otherwise TLB maintenance > * or update_mmu_cache() have the necessary barriers. > */ > if (pte_valid_not_user(pte)) { > dsb(ishst); > isb(); > } > } > > Thanks. >
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