| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <1B2017A4-A252-4C1F-9608-D43ECEAD53B1@nvidia.com>
Date: Wed, 08 May 2024 10:56:34 -0400
From: Zi Yan <ziy@...dia.com>
To: Lance Yang <ioworker0@...il.com>, Alistair Popple <apopple@...dia.com>,
Jason Gunthorpe <jgg@...dia.com>
Cc: akpm@...ux-foundation.org, willy@...radead.org, sj@...nel.org,
maskray@...gle.com, ryan.roberts@....com, david@...hat.com,
21cnbao@...il.com, mhocko@...e.com, fengwei.yin@...el.com,
zokeefe@...gle.com, shy828301@...il.com, xiehuan09@...il.com,
libang.li@...group.com, wangkefeng.wang@...wei.com, songmuchun@...edance.com,
peterx@...hat.com, minchan@...nel.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, Baolin Wang <baolin.wang@...ux.alibaba.com>
Subject: Re: [PATCH v4 2/3] mm/rmap: integrate PMD-mapped folio splitting into
pagewalk loop
On 8 May 2024, at 10:48, Zi Yan wrote:
> On 8 May 2024, at 10:35, Lance Yang wrote:
>
>> On Wed, May 8, 2024 at 10:07 PM Zi Yan <ziy@...dia.com> wrote:
>>>
>>> On 8 May 2024, at 1:43, Lance Yang wrote:
>>>
>>>> On Tue, May 7, 2024 at 11:26 PM Zi Yan <ziy@...dia.com> wrote:
>>>>>
>>>>> On 1 May 2024, at 0:26, Lance Yang wrote:
>>>>>
>>>>>> In preparation for supporting try_to_unmap_one() to unmap PMD-mapped
>>>>>> folios, start the pagewalk first, then call split_huge_pmd_address()
>>>>>> to split the folio.
>>>>>>
>>>>>> Suggested-by: David Hildenbrand <david@...hat.com>
>>>>>> Signed-off-by: Lance Yang <ioworker0@...il.com>
>>>>>> ---
>>>>>> include/linux/huge_mm.h | 20 ++++++++++++++++++++
>>>>>> mm/huge_memory.c | 42 +++++++++++++++++++++--------------------
>>>>>> mm/rmap.c | 24 +++++++++++++++++------
>>>>>> 3 files changed, 60 insertions(+), 26 deletions(-)
>>>>>>
>>>>>> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
>>>>>> index c8d3ec116e29..38c4b5537715 100644
>>>>>> --- a/include/linux/huge_mm.h
>>>>>> +++ b/include/linux/huge_mm.h
>>>>>> @@ -409,6 +409,20 @@ static inline bool thp_migration_supported(void)
>>>>>> return IS_ENABLED(CONFIG_ARCH_ENABLE_THP_MIGRATION);
>>>>>> }
>>>>>>
>>>>>> +void split_huge_pmd_locked(struct vm_area_struct *vma, unsigned long address,
>>>>>> + pmd_t *pmd, bool freeze, struct folio *folio);
>>>>>> +
>>>>>> +static inline void align_huge_pmd_range(struct vm_area_struct *vma,
>>>>>> + unsigned long *start,
>>>>>> + unsigned long *end)
>>>>>> +{
>>>>>> + *start = ALIGN(*start, HPAGE_PMD_SIZE);
>>>>>> + *end = ALIGN_DOWN(*end, HPAGE_PMD_SIZE);
>>>>>> +
>>>>>> + VM_WARN_ON_ONCE(vma->vm_start > *start);
>>>>>> + VM_WARN_ON_ONCE(vma->vm_end < *end);
>>>>>> +}
>>>>>> +
>>>>>> #else /* CONFIG_TRANSPARENT_HUGEPAGE */
>>>>>>
>>>>>> static inline bool folio_test_pmd_mappable(struct folio *folio)
>>>>>> @@ -471,6 +485,12 @@ static inline void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
>>>>>> unsigned long address, bool freeze, struct folio *folio) {}
>>>>>> static inline void split_huge_pmd_address(struct vm_area_struct *vma,
>>>>>> unsigned long address, bool freeze, struct folio *folio) {}
>>>>>> +static inline void split_huge_pmd_locked(struct vm_area_struct *vma,
>>>>>> + unsigned long address, pmd_t *pmd,
>>>>>> + bool freeze, struct folio *folio) {}
>>>>>> +static inline void align_huge_pmd_range(struct vm_area_struct *vma,
>>>>>> + unsigned long *start,
>>>>>> + unsigned long *end) {}
>>>>>>
>>>>>> #define split_huge_pud(__vma, __pmd, __address) \
>>>>>> do { } while (0)
>>>>>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>>>>>> index 8261b5669397..145505a1dd05 100644
>>>>>> --- a/mm/huge_memory.c
>>>>>> +++ b/mm/huge_memory.c
>>>>>> @@ -2584,6 +2584,27 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
>>>>>> pmd_populate(mm, pmd, pgtable);
>>>>>> }
>>>>>>
>>>>>> +void split_huge_pmd_locked(struct vm_area_struct *vma, unsigned long address,
>>>>>> + pmd_t *pmd, bool freeze, struct folio *folio)
>>>>>> +{
>>>>>> + VM_WARN_ON_ONCE(folio && !folio_test_pmd_mappable(folio));
>>>>>> + VM_WARN_ON_ONCE(!IS_ALIGNED(address, HPAGE_PMD_SIZE));
>>>>>> + VM_WARN_ON_ONCE(folio && !folio_test_locked(folio));
>>>>>> + VM_BUG_ON(freeze && !folio);
>>>>>> +
>>>>>> + /*
>>>>>> + * When the caller requests to set up a migration entry, we
>>>>>> + * require a folio to check the PMD against. Otherwise, there
>>>>>> + * is a risk of replacing the wrong folio.
>>>>>> + */
>>>>>> + if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd) ||
>>>>>> + is_pmd_migration_entry(*pmd)) {
>>>>>> + if (folio && folio != pmd_folio(*pmd))
>>>>>> + return;
>>>>>> + __split_huge_pmd_locked(vma, pmd, address, freeze);
>>>>>> + }
>>>>>> +}
>>>>>> +
>>>>>> void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
>>>>>> unsigned long address, bool freeze, struct folio *folio)
>>>>>> {
>>>>>> @@ -2595,26 +2616,7 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
>>>>>> (address & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE);
>>>>>> mmu_notifier_invalidate_range_start(&range);
>>>>>> ptl = pmd_lock(vma->vm_mm, pmd);
>>>>>> -
>>>>>> - /*
>>>>>> - * If caller asks to setup a migration entry, we need a folio to check
>>>>>> - * pmd against. Otherwise we can end up replacing wrong folio.
>>>>>> - */
>>>>>> - VM_BUG_ON(freeze && !folio);
>>>>>> - VM_WARN_ON_ONCE(folio && !folio_test_locked(folio));
>>>>>> -
>>>>>> - if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd) ||
>>>>>> - is_pmd_migration_entry(*pmd)) {
>>>>>> - /*
>>>>>> - * It's safe to call pmd_page when folio is set because it's
>>>>>> - * guaranteed that pmd is present.
>>>>>> - */
>>>>>> - if (folio && folio != pmd_folio(*pmd))
>>>>>> - goto out;
>>>>>> - __split_huge_pmd_locked(vma, pmd, range.start, freeze);
>>>>>> - }
>>>>>> -
>>>>>> -out:
>>>>>> + split_huge_pmd_locked(vma, range.start, pmd, freeze, folio);
>>>>>> spin_unlock(ptl);
>>>>>> mmu_notifier_invalidate_range_end(&range);
>>>>>> }
>>>>>> diff --git a/mm/rmap.c b/mm/rmap.c
>>>>>> index 7e2575d669a9..432601154583 100644
>>>>>> --- a/mm/rmap.c
>>>>>> +++ b/mm/rmap.c
>>>>>> @@ -1636,9 +1636,6 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
>>>>>> if (flags & TTU_SYNC)
>>>>>> pvmw.flags = PVMW_SYNC;
>>>>>>
>>>>>> - if (flags & TTU_SPLIT_HUGE_PMD)
>>>>>> - split_huge_pmd_address(vma, address, false, folio);
>>>>>> -
>>>>>> /*
>>>>>> * For THP, we have to assume the worse case ie pmd for invalidation.
>>>>>> * For hugetlb, it could be much worse if we need to do pud
>>>>>> @@ -1650,6 +1647,8 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
>>>>>> range.end = vma_address_end(&pvmw);
>>>>>> mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma->vm_mm,
>>>>>> address, range.end);
>>>>>> + if (flags & TTU_SPLIT_HUGE_PMD)
>>>>>> + align_huge_pmd_range(vma, &range.start, &range.end);
>>>>>> if (folio_test_hugetlb(folio)) {
>>>>>> /*
>>>>>> * If sharing is possible, start and end will be adjusted
>>>>>> @@ -1664,9 +1663,6 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
>>>>>> mmu_notifier_invalidate_range_start(&range);
>>>>>>
>>>>>> while (page_vma_mapped_walk(&pvmw)) {
>>>>>> - /* Unexpected PMD-mapped THP? */
>>>>>> - VM_BUG_ON_FOLIO(!pvmw.pte, folio);
>>>>>> -
>>>>>> /*
>>>>>> * If the folio is in an mlock()d vma, we must not swap it out.
>>>>>> */
>>>>>> @@ -1678,6 +1674,22 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
>>>>>> goto walk_done_err;
>>>>>> }
>>>>>>
>>>>>> + if (!pvmw.pte && (flags & TTU_SPLIT_HUGE_PMD)) {
>>>>>> + /*
>>>>>> + * We temporarily have to drop the PTL and start once
>>>>>> + * again from that now-PTE-mapped page table.
>>>>>> + */
>>>>>> + split_huge_pmd_locked(vma, range.start, pvmw.pmd, false,
>>>>>> + folio);
>>>>>
>>>>> Just in case you might miss here, since you will no longer align
>>>>> range.start as Baolin mentioned in another email and you have a VM_WARN_ONCE
>>>>> in split_huge_pmd_locked(), you will need to align the input address now.
>>>>
>>>> Thanks for bringing that up!
>>>>
>>>> I do miss the alignment here when I decide to no longer align range.start
>>>> in another email - thanks!
>>>>
>>> No problem.
>>>
>>>> Zi, could I move the alignment here?
>>>> IIUC, we will not encounter a partially mapped THP here, and range.start
>>>> and range.end should also not beyond the VMA limits.
>>>>
>>>> align_huge_pmd_range(vma, &range.start, &range.end);
>>>> split_huge_pmd_locked(vma, range.start, pvmw.pmd, false,
>>>> folio);
>>>
>>> I think you can just do
>>>
>>> split_huge_pmd_locked(vma, ALIGN(range.start, HPAGE_PMD_SIZE), pvmw.pmd, false, folio);
>>>
>>> since range will later be used by mmu_notifier_invalidate_range_end() and changing
>>> it might cause secondary TLB invalidation issues.
>>
>> Ok, makes sense to me - thanks!
>>
>> But we probably cannot use the HPAGE_PMD_SIZE here; it will cause
>> broken compilation as seen in v3[1].
>>
>> Perhaps we still need to add a new alignment function for the huge PMD?
>>
>> [1] https://lore.kernel.org/linux-mm/20240429202040.187453-1-sj@kernel.org/
>>
>> Thanks again for the review!
>>
> Or you can adjust the alignment inside split_huge_pmd_locked(), since it can
> be called other than __split_huge_pmd().
>
> Hmm, I notice that split_huge_pmd_address() has mmu_notifier ops but your
> split_huge_pmd_locked() does not include them, I wonder if that could cause
> issues with mmu_notifier issues. Adding mmu_notifier people to confirm.
Hi Alistair and Jason,
Lance is improving try_to_unmap_one() to support unmapping PMD THP as a whole,
so he moves split_huge_pmd_address() inside while (page_vma_mapped_walk(&pvmw))
and after mmu_notifier_invalidate_range_start() as split_huge_pmd_locked()
and does not include the mmu notifier ops inside split_huge_pmd_address().
I wonder if that could cause issues, since the mmu_notifier_invalidate_range_start()
before the while loop only has range of the original address and
split huge pmd can affect the entire PMD address range and these two ranges
might not be the same.
--
Best Regards,
Yan, Zi
Download attachment "signature.asc" of type "application/pgp-signature" (855 bytes)
Powered by blists - more mailing lists