From: Anshuman Khandual <anshuman.khandual@arm.com>
To: Samuel Holland <samuel.holland@sifive.com>,
Palmer Dabbelt <palmer@dabbelt.com>,
Paul Walmsley <pjw@kernel.org>,
linux-riscv@lists.infradead.org
Cc: devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, Conor Dooley <conor@kernel.org>,
Alexandre Ghiti <alex@ghiti.fr>,
Emil Renner Berthing <kernel@esmil.dk>,
Andrew Morton <akpm@linux-foundation.org>,
Rob Herring <robh+dt@kernel.org>,
Krzysztof Kozlowski <krzk+dt@kernel.org>
Subject: Re: [PATCH v2 04/18] mm: Always use page table accessor functions
Date: Thu, 9 Oct 2025 07:40:10 +0530 [thread overview]
Message-ID: <c6371fa1-af9c-47b0-988f-aae3d7fd58e7@arm.com> (raw)
In-Reply-To: <20251009015839.3460231-5-samuel.holland@sifive.com>
On 09/10/25 7:27 AM, Samuel Holland wrote:
> Some platforms need to fix up the values when reading or writing page
> tables. Because of this, the accessors must always be used; it is not
> valid to simply dereference a pXX_t pointer.
>
> Fix all of the instances of this pattern in generic code, mostly by
> applying the below coccinelle semantic patch, repeated for each page
> table level. Some additional fixes were applied manually, mostly to
> macros where type information is unavailable.
>
> In a few places, a `pte_t *` or `pmd_t *` is actually a pointer to a PTE
> or PMDE value stored on the stack, not a pointer to a page table. In
> those cases, it is not appropriate to use the accessors, because the
> value is not globally visible, and any transformation from pXXp_get()
> has already been applied. Those places are marked by naming the pointer
> `ptentp` or `pmdvalp`, as opposed to `ptep` or `pmdp`.
>
> @@
> pte_t *P;
> expression E;
> expression I;
> @@
> - P[I] = E
> + set_pte(P + I, E)
>
> @@
> pte_t *P;
> expression E;
> @@
> (
> - WRITE_ONCE(*P, E)
> + set_pte(P, E)
> |
> - *P = E
> + set_pte(P, E)
> )
>
> @@
> pte_t *P;
> expression I;
> @@
> (
> &P[I]
> |
> - READ_ONCE(P[I])
> + ptep_get(P + I)
> |
> - P[I]
> + ptep_get(P + I)
> )
>
> @@
> pte_t *P;
> @@
> (
> - READ_ONCE(*P)
> + ptep_get(P)
> |
> - *P
> + ptep_get(P)
> )
>
> Additionally, the following semantic patch was used to convert PMD and
> PUD references inside struct vm_fault:
>
> @@
> struct vm_fault vmf;
> @@
> (
> - *vmf.pmd
> + pmdp_get(vmf.pmd)
> |
> - *vmf.pud
> + pudp_get(vmf.pud)
> )
>
> @@
> struct vm_fault *vmf;
> @@
> (
> - *vmf->pmd
> + pmdp_get(vmf->pmd)
> |
> - *vmf->pud
> + pudp_get(vmf->pud)
> )
>
> Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
> ---
> This commit covers some of the same changes as an existing series from
> Anshuman Khandual[1]. Unlike that series, this commit is a purely
> mechanical conversion to demonstrate the RISC-V changes, so it does not
> insert local variables to avoid redundant calls to the accessors. A
> manual conversion like in that series could improve performance.
>
> [1]: https://lore.kernel.org/linux-mm/20240917073117.1531207-1-anshuman.khandual@arm.com/
Portions of the changes proposed here are already in discussion
and fetched for testing via mm-new/everything.
https://lore.kernel.org/linux-mm/20251007063100.2396936-1-anshuman.khandual@arm.com/
https://lore.kernel.org/linux-mm/20251006055214.1845342-1-anshuman.khandual@arm.com/
next prev parent reply other threads:[~2025-10-09 2:10 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-10-09 1:57 [PATCH v2 00/18] riscv: Memory type control for platforms with physical memory aliases Samuel Holland
2025-10-09 1:57 ` [PATCH v2 01/18] mm/ptdump: Replace READ_ONCE() with standard page table accessors Samuel Holland
2025-10-09 9:34 ` David Hildenbrand
2025-10-09 1:57 ` [PATCH v2 02/18] perf/core: " Samuel Holland
2025-10-09 2:03 ` Anshuman Khandual
2025-10-09 1:57 ` [PATCH v2 03/18] mm: Move the fallback definitions of pXXp_get() Samuel Holland
2025-10-09 1:57 ` [PATCH v2 04/18] mm: Always use page table accessor functions Samuel Holland
2025-10-09 2:10 ` Anshuman Khandual [this message]
2025-10-09 1:57 ` [PATCH v2 05/18] mm: Allow page table accessors to be non-idempotent Samuel Holland
2025-10-09 1:57 ` [PATCH v2 06/18] riscv: hibernate: Replace open-coded pXXp_get() Samuel Holland
2025-10-09 1:57 ` [PATCH v2 07/18] riscv: mm: Always use page table accessor functions Samuel Holland
2025-10-09 1:57 ` [PATCH v2 08/18] riscv: mm: Simplify set_p4d() and set_pgd() Samuel Holland
2025-10-09 1:57 ` [PATCH v2 09/18] riscv: mm: Deduplicate _PAGE_CHG_MASK definition Samuel Holland
2025-10-09 1:57 ` [PATCH v2 10/18] riscv: ptdump: Only show N and MT bits when enabled in the kernel Samuel Holland
2025-10-09 1:57 ` [PATCH v2 11/18] riscv: mm: Fix up memory types when writing page tables Samuel Holland
2025-10-09 1:57 ` [PATCH v2 12/18] riscv: mm: Expose all page table bits to assembly code Samuel Holland
2025-10-09 1:57 ` [PATCH v2 13/18] riscv: alternative: Add an ALTERNATIVE_3 macro Samuel Holland
2025-10-09 1:57 ` [PATCH v2 14/18] riscv: alternative: Allow calls with alternate link registers Samuel Holland
2025-10-09 1:57 ` [PATCH v2 15/18] dt-bindings: riscv: Describe physical memory regions Samuel Holland
2025-10-09 12:37 ` Rob Herring (Arm)
2025-10-09 1:57 ` [PATCH v2 16/18] riscv: mm: Use physical memory aliases to apply PMAs Samuel Holland
2025-10-10 15:06 ` Emil Renner Berthing
2025-10-10 16:12 ` Samuel Holland
2025-10-10 17:04 ` Emil Renner Berthing
2025-10-10 18:01 ` Samuel Holland
2025-10-10 19:55 ` Emil Renner Berthing
2025-10-09 1:57 ` [PATCH v2 17/18] riscv: dts: starfive: jh7100: Use physical memory ranges for DMA Samuel Holland
2025-10-10 14:19 ` Emil Renner Berthing
2025-10-10 16:51 ` Samuel Holland
2025-10-14 9:14 ` Conor Dooley
2025-10-09 1:57 ` [PATCH v2 18/18] riscv: dts: eswin: eic7700: " Samuel Holland
2025-10-10 1:15 ` [PATCH v2 00/18] riscv: Memory type control for platforms with physical memory aliases Andrew Morton
2025-10-10 17:17 ` Samuel Holland
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=c6371fa1-af9c-47b0-988f-aae3d7fd58e7@arm.com \
--to=anshuman.khandual@arm.com \
--cc=akpm@linux-foundation.org \
--cc=alex@ghiti.fr \
--cc=conor@kernel.org \
--cc=devicetree@vger.kernel.org \
--cc=kernel@esmil.dk \
--cc=krzk+dt@kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=linux-riscv@lists.infradead.org \
--cc=palmer@dabbelt.com \
--cc=pjw@kernel.org \
--cc=robh+dt@kernel.org \
--cc=samuel.holland@sifive.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).