On 2022/8/17 10:53, Muchun Song wrote:
>
>
>> On Aug 16, 2022, at 21:05, Miaohe Lin <linmiaohe@xxxxxxxxxx> 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.
>
