linux-kernel - Re: [PATCH v5 07/12] mm: bail out of lazy_mmu_mode

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Message-ID: <9800804f-6e8a-4d08-8eb1-f114df6d6b7a@kernel.org>
Date: Mon, 24 Nov 2025 15:11:44 +0100
From: "David Hildenbrand (Red Hat)" <david@...nel.org>
To: Kevin Brodsky <kevin.brodsky@....com>, linux-mm@...ck.org
Cc: 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 S. Miller" <davem@...emloft.net>,
 David Woodhouse <dwmw2@...radead.org>, "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>,
 "Ritesh Harjani (IBM)" <ritesh.list@...il.com>,
 Ryan Roberts <ryan.roberts@....com>, Suren Baghdasaryan <surenb@...gle.com>,
 Thomas Gleixner <tglx@...utronix.de>,
 Venkat Rao Bagalkote <venkat88@...ux.ibm.com>,
 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, x86@...nel.org
Subject: Re: [PATCH v5 07/12] mm: bail out of lazy_mmu_mode_* in interrupt
 context

On 11/24/25 14:22, Kevin Brodsky wrote:
> The lazy MMU mode cannot be used in interrupt context. This is
> documented in <linux/pgtable.h>, but isn't consistently handled
> across architectures.
> 
> arm64 ensures that calls to lazy_mmu_mode_* have no effect in
> interrupt context, because such calls do occur in certain
> configurations - see commit b81c688426a9 ("arm64/mm: Disable barrier
> batching in interrupt contexts"). Other architectures do not check
> this situation, most likely because it hasn't occurred so far.
> 
> Let's handle this in the new generic lazy_mmu layer, in the same
> fashion as arm64: bail out of lazy_mmu_mode_* if in_interrupt().
> Also remove the arm64 handling that is now redundant.
> 
> Both arm64 and x86/Xen also ensure that any lazy MMU optimisation is
> disabled while in interrupt (see queue_pte_barriers() and
> xen_get_lazy_mode() respectively). This will be handled in the
> generic layer in a subsequent patch.
> 
> Signed-off-by: Kevin Brodsky <kevin.brodsky@....com>
> ---

(resending as I pushed the wrong button there ...)

Moving this patch earlier LGTM, hoping we don't get any unexpected
surprises ...

Acked-by: David Hildenbrand (Red Hat) <david@...nel.org>

-- 
Cheers

David