linux-kernel - Re: [PATCH v17 00/12] Support page table check on PowerPC

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Message-Id: <20250925161726.2b34890070e6d8dcf8ad3ba9@linux-foundation.org>
Date: Thu, 25 Sep 2025 16:17:26 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Andrew Donnellan <ajd@...ux.ibm.com>
Cc: linuxppc-dev@...ts.ozlabs.org, linux-mm@...ck.org, x86@...nel.org,
 linux-riscv@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org, pasha.tatashin@...een.com,
 sweettea-kernel@...miny.me, nicholas@...ux.ibm.com,
 christophe.leroy@...roup.eu, alexghiti@...osinc.com
Subject: Re: [PATCH v17 00/12] Support page table check on PowerPC

On Fri, 26 Sep 2025 08:42:35 +1000 Andrew Donnellan <ajd@...ux.ibm.com> wrote:

> On Tue, 2025-09-09 at 19:13 +1000, Andrew Donnellan wrote:
> > Support page table check on all PowerPC platforms. This works by serialising
> > assignments, reassignments and clears of page table entries at each level in
> > order 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.
> > 
> > Note that on 32 bit systems with CONFIG_KFENCE=y, you need [0] to avoid
> > possible failures in init code (this is a code patching/static keys issue,
> > which was discovered by a user testing this series but isn't a bug in page
> > table check).
> > 
> > (This series was initially written by Rohan McLure, who has left IBM and
> > is no longer working on powerpc.)
> 
> Is this likely to make it in in time for 6.18, or should I respin it post merge
> window?

The latter, please.