linux-kernel - Re: [PATCH v2 0/7] Nesting support for lazy MMU mode

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Message-ID: <c07b8a65-7cef-4ddd-bd94-d2e275edc2a8@lucifer.local>
Date: Mon, 8 Sep 2025 17:56:05 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Kevin Brodsky <kevin.brodsky@....com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        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 Hildenbrand <david@...hat.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>,
        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
Subject: Re: [PATCH v2 0/7] Nesting support for lazy MMU mode


On Mon, Sep 08, 2025 at 08:39:24AM +0100, Kevin Brodsky wrote:
> When the lazy MMU mode was introduced eons ago, it wasn't made clear
> whether such a sequence was legal:
>
> 	arch_enter_lazy_mmu_mode()
> 	...
> 		arch_enter_lazy_mmu_mode()
> 		...
> 		arch_leave_lazy_mmu_mode()
> 	...
> 	arch_leave_lazy_mmu_mode()
>
> It seems fair to say that nested calls to
> arch_{enter,leave}_lazy_mmu_mode() were not expected, and most
> architectures never explicitly supported it.


This is compiling with CONFIG_USERFAULTFD at all commits and series is
compiling with allmodconfig plus all mm selftests are passing so from my
side this looks good, thanks for addressing issues and rebasing! :)

Cheers, Lorenzo