From: Muchun Song <muchun.song@linux.dev>
To: Miaohe Lin <linmiaohe@huawei.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Mike Kravetz <mike.kravetz@oracle.com>,
Muchun Song <songmuchun@bytedance.com>,
Linux MM <linux-mm@kvack.org>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 4/6] mm: hugetlb_vmemmap: add missing smp_wmb() before set_pte_at()
Date: Wed, 17 Aug 2022 19:21:20 +0800 [thread overview]
Message-ID: <0EAF1279-6A1C-41FA-9A32-414C36B3792A@linux.dev> (raw)
In-Reply-To: <ea67ab10-667e-f361-b80f-dafb13da4808@huawei.com>
> On Aug 17, 2022, at 16:41, Miaohe Lin <linmiaohe@huawei.com> wrote:
>
> 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);
IIUC, the case here we should make sure others (CPUs) can see new page’s
contents after they have saw PG_uptodate is set. I think commit 0ed361dec369
can tell us more details.
I also looked at commit 52f37629fd3c to see why we need a barrier before
set_pte_at(), but I didn’t find any info to explain why. I guess we want
to make sure the order between the page’s contents and subsequent memory
accesses using the corresponding virtual address, do you agree with this?
Thanks.
>
> 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.
>>
next prev parent reply other threads:[~2022-08-17 11:21 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-16 13:05 [PATCH 0/6] A few fixup patches for hugetlb Miaohe Lin
2022-08-16 13:05 ` [PATCH 1/6] mm/hugetlb: fix incorrect update of max_huge_pages Miaohe Lin
2022-08-16 22:52 ` Mike Kravetz
2022-08-16 23:20 ` Andrew Morton
2022-08-16 23:34 ` Mike Kravetz
2022-08-17 1:53 ` Miaohe Lin
2022-08-17 2:28 ` Muchun Song
2022-08-16 13:05 ` [PATCH 2/6] mm/hugetlb: fix WARN_ON(!kobj) in sysfs_create_group() Miaohe Lin
2022-08-16 22:55 ` Mike Kravetz
2022-08-17 2:31 ` Muchun Song
2022-08-17 2:39 ` Miaohe Lin
2022-08-16 13:05 ` [PATCH 3/6] mm/hugetlb: fix missing call to restore_reserve_on_error() Miaohe Lin
2022-08-16 23:31 ` Mike Kravetz
2022-08-17 1:59 ` Miaohe Lin
2022-08-16 13:05 ` [PATCH 4/6] mm: hugetlb_vmemmap: add missing smp_wmb() before set_pte_at() Miaohe Lin
2022-08-17 2:53 ` Muchun Song
2022-08-17 8:41 ` Miaohe Lin
2022-08-17 9:13 ` Yin, Fengwei
2022-08-17 11:21 ` Muchun Song [this message]
2022-08-18 1:14 ` Yin, Fengwei
2022-08-18 1:55 ` Miaohe Lin
2022-08-18 2:00 ` Yin, Fengwei
2022-08-18 2:47 ` Muchun Song
2022-08-18 7:52 ` Miaohe Lin
2022-08-18 7:59 ` Muchun Song
2022-08-18 8:32 ` Yin, Fengwei
2022-08-18 8:40 ` Muchun Song
2022-08-18 8:54 ` Yin, Fengwei
2022-08-18 9:18 ` Muchun Song
2022-08-18 12:58 ` Miaohe Lin
2022-08-18 23:53 ` Yin, Fengwei
2022-08-19 3:19 ` Muchun Song
2022-08-19 7:26 ` Miaohe Lin
2022-08-18 1:15 ` Yin, Fengwei
2022-08-20 8:12 ` Muchun Song
2022-08-22 8:45 ` Miaohe Lin
2022-08-22 10:23 ` Muchun Song
2022-08-23 1:42 ` Miaohe Lin
2022-08-16 13:05 ` [PATCH 5/6] mm/hugetlb: fix sysfs group leak in hugetlb_unregister_node() Miaohe Lin
2022-08-17 9:41 ` Yin, Fengwei
2022-08-18 1:00 ` Yin, Fengwei
2022-08-18 1:12 ` Yin, Fengwei
2022-08-16 13:05 ` [PATCH 6/6] mm/hugetlb: make detecting shared pte more reliable Miaohe Lin
2022-08-17 23:56 ` Mike Kravetz
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