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

Message-ID: <5afabf30-da5f-4fa8-b1c2-e3b384c2d99c@lucifer.local>
Date: Mon, 9 Jun 2025 16:08:55 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Qi Zheng <zhengqi.arch@...edance.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>,
        David Hildenbrand <david@...hat.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 Mon, Jun 09, 2025 at 02:40:09PM +0800, 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.

Oh interesting... will note down for when I take a look should you not get to it
first :>)

>
> >
> > Overall - I will stash this response somewhere and come back to it if
> > somebody else doesn't in the meantime :)
>
> Thanks!
>
> >
> > >
>
>

Cheers, Lorenzo