linux-kernel - Re: [PATCH RFC v2] mm: use per_vma lock for MADV

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] [day] [month] [year] [list]

Message-ID: <06369558-6b58-4e0f-9f5d-e50dc693d53f@redhat.com>
Date: Tue, 10 Jun 2025 09:20:02 +0200
From: David Hildenbrand <david@...hat.com>
To: Qi Zheng <zhengqi.arch@...edance.com>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Jann Horn <jannh@...gle.com>, Barry Song <21cnbao@...il.com>,
 akpm@...ux-foundation.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 Barry Song <v-songbaohua@...o.com>, "Liam R. Howlett"
 <Liam.Howlett@...cle.com>, Vlastimil Babka <vbabka@...e.cz>,
 Suren Baghdasaryan <surenb@...gle.com>, Lokesh Gidra
 <lokeshgidra@...gle.com>, Tangquan Zheng <zhengtangquan@...o.com>
Subject: Re: [PATCH RFC v2] mm: use per_vma lock for MADV_DONTNEED

On 09.06.25 08:40, Qi Zheng wrote:
> Hi Lorenzo,
> 
> On 6/6/25 6:44 PM, Lorenzo Stoakes wrote:
> 
> [snip]
> 
>>>
>>>>
>>>> We could in theory always add another callback .pmd_entry_sleep or
>>>> something for this one case and document the requirement...
>>>
>>> Maybe, but the SRCU critical section cannot prevent the PTE page from
>>> being freed via RCU. :(
>>
>> Idea is we'd fall back to non-RCU in this case and take locks... but then
>> ugh we'd race everything RCU and no it's all or nothing isn't it?
> 
> So maybe the RCU+refcount method is feasible. We can release the RCU
> lock after incrementing the reference count, which can ensure that the
> page table page is not freed.

I'll not that maybe after the memdesc rework, page tables will no longer 
have a refcount. Maybe.

I mean, it kind-of makes sense, because nobody should really be taking 
references on page table.

So finding something that doesn't depend on page-table refcounts might 
be better.

-- 
Cheers,

David / dhildenb