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

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

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1c527333-e837-4a40-afa8-eb8728332055@redhat.com>
Date: Tue, 30 Jul 2024 23:19:27 +0200
From: David Hildenbrand <david@...hat.com>
To: James Houghton <jthoughton@...gle.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 30.07.24 23:17, James Houghton wrote:
> On Tue, Jul 30, 2024 at 2:07 PM David Hildenbrand <david@...hat.com> wrote:
>>
>> On 30.07.24 23:00, David Hildenbrand wrote:
>>> On 30.07.24 22:43, James Houghton wrote:
>>>> 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,
>>>>
>>>
>>> Hi!
>>>
>>>> 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.
>>>
>>> I thought I convinced myself that leaf page tables are always single
>>> pages and had a comment in v1.
>>>
>>> But now I have to double-check again, and staring at
>>> pagetable_pte_ctor() callers I am left confused.
>>>
>>> It certainly sounds more future proof to just align the pointer down to
>>> the start of the PTE table like pmd_lockptr() would.
>>>
>>>> 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.)
>>>
>>> It's a valid concern even if it would not be required. But I'm afraid I
>>> won't dig into the details and simply do the alignment in a v3.
>>
>> To be precise, the following on top:
>>
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index 1b1f40ff00b7d..f6c7fe8f5746f 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -2926,10 +2926,22 @@ 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)
>> +static inline struct page *ptep_pgtable_page(pte_t *pte)
>>    {
>> +       unsigned long mask = ~(PTRS_PER_PTE * sizeof(pte_t) - 1);
>> +
>>           BUILD_BUG_ON(IS_ENABLED(CONFIG_HIGHPTE));
>> -       return ptlock_ptr(virt_to_ptdesc(pte));
>> +       return virt_to_page((void *)((unsigned long)pte & mask));
>> +}
>> +
>> +static inline struct ptdesc *ptep_ptdesc(pte_t *pte)
>> +{
>> +       return page_ptdesc(ptep_pgtable_page(pte));
>> +}
>> +
>> +static inline spinlock_t *ptep_lockptr(struct mm_struct *mm, pte_t *pte)
>> +{
>> +       return ptlock_ptr(ptep_ptdesc(pte));
>>    }
> 
> Thanks! That looks right to me. Feel free to add
> 
> Reviewed-by: James Houghton <jthoughton@...gle.com>

Thanks for the review, will send a v3 tomorrow after having wasted more 
valuable life time setting up the ARM environment again ... :)

-- 
Cheers,

David / dhildenb