From: "David Hildenbrand (Red Hat)" <david@kernel.org>
To: Ryan Roberts <ryan.roberts@arm.com>,
Samuel Holland <samuel.holland@sifive.com>,
Palmer Dabbelt <palmer@dabbelt.com>,
Paul Walmsley <pjw@kernel.org>,
linux-riscv@lists.infradead.org,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org
Cc: devicetree@vger.kernel.org,
Suren Baghdasaryan <surenb@google.com>,
linux-kernel@vger.kernel.org, Mike Rapoport <rppt@kernel.org>,
Michal Hocko <mhocko@suse.com>, Conor Dooley <conor@kernel.org>,
Lorenzo Stoakes <lorenzo.stoakes@oracle.com>,
Krzysztof Kozlowski <krzk+dt@kernel.org>,
Alexandre Ghiti <alex@ghiti.fr>,
Emil Renner Berthing <kernel@esmil.dk>,
Rob Herring <robh+dt@kernel.org>,
Vlastimil Babka <vbabka@suse.cz>,
"Liam R . Howlett" <Liam.Howlett@oracle.com>
Subject: Re: [PATCH v3 08/22] mm: Allow page table accessors to be non-idempotent
Date: Thu, 27 Nov 2025 18:47:38 +0100 [thread overview]
Message-ID: <c2597d43-d909-4259-bb5b-9294e4069385@kernel.org> (raw)
In-Reply-To: <fbfef7fc-4030-462b-b514-498eea6620aa@arm.com>
On 11/27/25 17:57, Ryan Roberts wrote:
> On 13/11/2025 01:45, Samuel Holland wrote:
>> Currently, some functions such as pte_offset_map() are passed both
>> pointers to hardware page tables, and pointers to previously-read PMD
>> entries on the stack. To ensure correctness in the first case, these
>> functions must use the page table accessor function (pmdp_get()) to
>> dereference the supplied pointer. However, this means pmdp_get() is
>> called twice in the second case. This double call must be avoided if
>> pmdp_get() applies some non-idempotent transformation to the value.
>>
>> Avoid the double transformation by calling set_pmd() on the stack
>> variables where necessary to keep set_pmd()/pmdp_get() calls balanced.
>
> I don't think this is a good solution.
Agreed,
set_pmd(&pmd, pmd);
is rather horrible.
--
Cheers
David
next prev parent reply other threads:[~2025-11-27 17:47 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-11-13 1:45 [PATCH v3 00/22] riscv: Memory type control for platforms with physical memory aliases Samuel Holland
2025-11-13 1:45 ` [PATCH v3 01/22] mm/ptdump: replace READ_ONCE() with standard page table accessors Samuel Holland
2025-11-13 1:45 ` [PATCH v3 02/22] mm: " Samuel Holland
2025-11-13 4:05 ` Dev Jain
2025-11-13 1:45 ` [PATCH v3 03/22] mm/dirty: replace READ_ONCE() with pudp_get() Samuel Holland
2025-11-13 1:45 ` [PATCH v3 04/22] perf/events: replace READ_ONCE() with standard page table accessors Samuel Holland
2025-11-13 19:10 ` David Hildenbrand (Red Hat)
2025-11-13 1:45 ` [PATCH v3 05/22] mm: Move the fallback definitions of pXXp_get() Samuel Holland
2025-11-13 19:11 ` David Hildenbrand (Red Hat)
2025-11-13 1:45 ` [PATCH v3 06/22] mm: Always use page table accessor functions Samuel Holland
2025-11-13 4:53 ` kernel test robot
2025-11-13 5:46 ` kernel test robot
2025-11-26 11:08 ` Christophe Leroy (CS GROUP)
2025-11-26 11:09 ` Ryan Roberts
2025-11-26 12:16 ` David Hildenbrand (Red Hat)
2025-11-26 12:19 ` David Hildenbrand (Red Hat)
2025-11-26 12:27 ` Lorenzo Stoakes
2025-11-26 12:35 ` David Hildenbrand (Red Hat)
2025-11-26 13:03 ` Ryan Roberts
2025-11-26 13:47 ` Wei Yang
2025-11-26 14:22 ` Ryan Roberts
2025-11-26 14:37 ` Lorenzo Stoakes
2025-11-26 14:53 ` David Hildenbrand (Red Hat)
2025-11-26 14:46 ` David Hildenbrand (Red Hat)
2025-11-26 14:52 ` Lorenzo Stoakes
2025-11-26 14:56 ` David Hildenbrand (Red Hat)
2025-11-26 15:08 ` Lorenzo Stoakes
2025-11-26 15:12 ` David Hildenbrand (Red Hat)
2025-11-26 16:07 ` Ryan Roberts
2025-11-26 16:34 ` Ryan Roberts
2025-11-26 20:31 ` David Hildenbrand (Red Hat)
2025-11-27 7:14 ` David Hildenbrand (Red Hat)
2025-11-27 7:31 ` David Hildenbrand (Red Hat)
2025-11-27 15:32 ` Ryan Roberts
2025-11-27 19:39 ` Christophe Leroy (CS GROUP)
2025-11-27 19:44 ` Christophe Leroy (CS GROUP)
2025-11-27 8:26 ` Christophe Leroy (CS GROUP)
2025-11-27 8:35 ` David Hildenbrand (Red Hat)
2025-11-13 1:45 ` [PATCH v3 07/22] checkpatch: Warn on page table access without accessors Samuel Holland
2025-11-13 2:21 ` Joe Perches
2025-11-13 2:36 ` Samuel Holland
2025-11-13 19:17 ` David Hildenbrand (Red Hat)
2025-11-13 1:45 ` [PATCH v3 08/22] mm: Allow page table accessors to be non-idempotent Samuel Holland
2025-11-13 7:19 ` kernel test robot
2025-11-27 16:57 ` Ryan Roberts
2025-11-27 17:47 ` David Hildenbrand (Red Hat) [this message]
2025-11-13 1:45 ` [PATCH v3 09/22] riscv: hibernate: Replace open-coded pXXp_get() Samuel Holland
2025-11-13 1:45 ` [PATCH v3 10/22] riscv: mm: Always use page table accessor functions Samuel Holland
2025-11-13 1:45 ` [PATCH v3 11/22] riscv: mm: Simplify set_p4d() and set_pgd() Samuel Holland
2025-11-13 1:45 ` [PATCH v3 12/22] riscv: mm: Deduplicate _PAGE_CHG_MASK definition Samuel Holland
2025-11-13 1:45 ` [PATCH v3 13/22] riscv: ptdump: Only show N and MT bits when enabled in the kernel Samuel Holland
2025-11-13 1:45 ` [PATCH v3 14/22] riscv: mm: Fix up memory types when writing page tables Samuel Holland
2025-11-13 1:45 ` [PATCH v3 15/22] riscv: mm: Expose all page table bits to assembly code Samuel Holland
2025-11-13 1:45 ` [PATCH v3 16/22] riscv: alternative: Add an ALTERNATIVE_3 macro Samuel Holland
2025-11-13 1:45 ` [PATCH v3 17/22] riscv: alternative: Allow calls with alternate link registers Samuel Holland
2025-11-13 1:45 ` [PATCH v3 18/22] riscv: Fix logic for selecting DMA_DIRECT_REMAP Samuel Holland
2025-11-13 1:45 ` [PATCH v3 19/22] dt-bindings: riscv: Describe physical memory regions Samuel Holland
2025-12-04 15:12 ` Rob Herring
2025-11-13 1:45 ` [PATCH v3 20/22] riscv: mm: Use physical memory aliases to apply PMAs Samuel Holland
2025-11-13 1:45 ` [PATCH v3 21/22] riscv: dts: starfive: jh7100: Use physical memory ranges for DMA Samuel Holland
2025-11-13 1:45 ` [PATCH v3 22/22] riscv: dts: eswin: eic7700: " Samuel Holland
2025-11-13 19:13 ` [PATCH v3 00/22] riscv: Memory type control for platforms with physical memory aliases David Hildenbrand (Red Hat)
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