linux-kernel - Re: [PATCH v2 2/7] mm: introduce local state for lazy

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: <f9b0bf10-a531-484e-9679-08ec25ceb444@arm.com>
Date: Fri, 12 Sep 2025 17:02:34 +0200
From: Kevin Brodsky <kevin.brodsky@....com>
To: David Hildenbrand <david@...hat.com>,
 Alexander Gordeev <agordeev@...ux.ibm.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 Andreas Larsson <andreas@...sler.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Boris Ostrovsky <boris.ostrovsky@...cle.com>, Borislav Petkov
 <bp@...en8.de>, Catalin Marinas <catalin.marinas@....com>,
 Christophe Leroy <christophe.leroy@...roup.eu>,
 Dave Hansen <dave.hansen@...ux.intel.com>,
 "David S. Miller" <davem@...emloft.net>, "H. Peter Anvin" <hpa@...or.com>,
 Ingo Molnar <mingo@...hat.com>, Jann Horn <jannh@...gle.com>,
 Juergen Gross <jgross@...e.com>, "Liam R. Howlett"
 <Liam.Howlett@...cle.com>, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Madhavan Srinivasan <maddy@...ux.ibm.com>,
 Michael Ellerman <mpe@...erman.id.au>, Michal Hocko <mhocko@...e.com>,
 Mike Rapoport <rppt@...nel.org>, Nicholas Piggin <npiggin@...il.com>,
 Peter Zijlstra <peterz@...radead.org>, Ryan Roberts <ryan.roberts@....com>,
 Suren Baghdasaryan <surenb@...gle.com>, Thomas Gleixner
 <tglx@...utronix.de>, Vlastimil Babka <vbabka@...e.cz>,
 Will Deacon <will@...nel.org>, Yeoreum Yun <yeoreum.yun@....com>,
 linux-arm-kernel@...ts.infradead.org, linuxppc-dev@...ts.ozlabs.org,
 sparclinux@...r.kernel.org, xen-devel@...ts.xenproject.org,
 Mark Rutland <Mark.Rutland@....com>
Subject: Re: [PATCH v2 2/7] mm: introduce local state for lazy_mmu sections

On 12/09/2025 16:25, David Hildenbrand wrote:
>
>>
>> But I do not really expect it ever, since arch_enter_lazy_mmu_mode_pte()
>> is only to be called in PTE walkers that never span more than one page
>> table and follow the pattern:
>
> Well, the cover letter here states:
>
> "Unfortunately, a corner case (DEBUG_PAGEALLOC) may still cause
> nesting to occur on arm64. Ryan proposed [2] to address that corner
> case at the generic level but this approach received pushback; [3]
> then attempted to solve the issue on arm64 only, but it was deemed too
> fragile."
>
> So I guess we should support nesting cleanly, at least on the core-mm
> side.

Nesting remains a rare occurrence though. I think it would be plausible
to require this new interface to be used in a region where no nesting
can occur, just like pause()/resume().

In fact, I think this is a requirement if we go for the approach we have
been discussing, because nested enter()/leave() calls are not meant to
call arch_enter()/arch_leave(), and I really wouldn't want to use a
different logic for this variant.

>
> I guess we could start with saying "well, s390x doesn't fully support
> nesting yet but doing so just requires changing the way we manage this
> per-nesting-level state internally".
>
> s390 is trying to do something different than the other archs here, so
> that naturally concerns me :)
>
> But if it's really just about forwarding that data and having s390
> store it somewhere (task_struct, percpu variable, etc), fine with me. 

Yes I think this is fine, with the restriction above. The extra
arguments are directly forwarded to arch code and otherwise ignored by
core code, and unless the arch defines some __HAVE_ARCH... or CONFIG,
the extended interface falls back to regular enter()/leave().

- Kevin