linux-kernel - Re: [PATCH v18 00/12] Support page table check on PowerPC

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Message-ID: <CA+CK2bBjoQmheEstv1MacGev_srdx=m5v=hwxdyfAKogbpG3FA@mail.gmail.com>
Date: Thu, 18 Dec 2025 12:55:45 -0500
From: Pasha Tatashin <pasha.tatashin@...een.com>
To: Andrew Donnellan <ajd@...ux.ibm.com>
Cc: linux-mm@...ck.org, linuxppc-dev@...ts.ozlabs.org, 
	Andrew Morton <akpm@...ux-foundation.org>, Madhavan Srinivasan <maddy@...ux.ibm.com>, 
	Nicholas Piggin <npiggin@...il.com>, Rohan McLure <rmclure@...dia.com>, 
	Christophe Leroy <chleroy@...nel.org>, Alexandre Ghiti <alex@...ti.fr>, x86@...nel.org, 
	Nicholas Miehlbradt <nicholas@...ux.ibm.com>, Sweet Tea Dorminy <sweettea-kernel@...miny.me>, 
	Andrew Donnellan <andrew+kernel@...nellan.id.au>, Srish Srinivasan <ssrish@...ux.ibm.com>, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v18 00/12] Support page table check on PowerPC

On Thu, Dec 18, 2025 at 12:10 PM Andrew Donnellan <ajd@...ux.ibm.com> wrote:
>
> [I will be leaving IBM in about a month from now, and will also be on leave
> for most of that time starting tomorrow. I've cc'd my personal email, which
> I am going to use for any kernel development I do after I leave, and also
> Srish Srinivasan, who will be taking over some of my work.]
>
> Support page table check on PowerPC. Page table check tracks the usage of
> of page table entries at each level to ensure that anonymous mappings have
> at most one writable consumer, and likewise that file-backed mappings are
> not simultaneously also anonymous mappings.
>
> In order to support this infrastructure, a number of helpers or stubs must be
> defined or updated for all powerpc platforms. Additionally, we separate
> set_pte_at() and set_pte_at_unchecked(), to allow for internal, uninstrumented
> mappings.
>
> On some PowerPC platforms, implementing {pte,pmd,pud}_user_accessible_page()
> requires the address. We revert previous changes that removed the address
> parameter from various interfaces, and add it to some other interfaces,
> in order to allow this.
>
> For now, we don't allow page table check alongside HUGETLB_PAGE, due to the
> arch-specific complexity of set_huge_page_at(). (I'm sure I could figure
> this out, but I have to get this version on this list before I leave my job.)
>
> This series was initially written by Rohan McLure, who has left IBM and
> is no longer working on powerpc.
>
> v18:
>  * Rebase on mm-new
>  * Add instrumentation for pudp_invalidate()
>  * Add cleanup patch to use pte_advance_pfn()
>  * Move p{m,u}d_user_accessible_page() to a more sensible place in the code
>  * Disable when HUGETLB_PAGE is enabled

Thank you. This series looks good to me.

Pasha