linux-kernel - [RFC 0/2] mm/ptdump: Drop assumption that pxd

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Message-Id: <20250310095902.390664-1-anshuman.khandual@arm.com>
Date: Mon, 10 Mar 2025 15:29:00 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: linux-mm@...ck.org
Cc: Anshuman Khandual <anshuman.khandual@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Madhavan Srinivasan <maddy@...ux.ibm.com>,
	Nicholas Piggin <npiggin@...il.com>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
	Heiko Carstens <hca@...ux.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org,
	linux-riscv@...ts.infradead.org,
	linux-s390@...r.kernel.org
Subject: [RFC 0/2] mm/ptdump: Drop assumption that pxd_val() is u64

Last argument passed down in note_page() is u64 assuming pxd_val() returned
value (all page table levels) is 64 bit - which might not be the case going
ahead when D128 page tables is enabled on arm64 platform. Besides pxd_val()
is very platform specific and its type should not be assumed in generic MM.

This series splits note_page() into individual page table level specific
callbacks which accepts corresponding pxd_t page table entry as an argument
instead and later all subscribing platforms could derive pxd_val() from the
entries as required and proceed as before.

Page table entry's value, mask and protection are represented with pteval_t
not u64 that has been assumed while dumping the page table entries on arm64
platform. Replace such u64 instances with pteval_t instead as expected.

This series has been lightly tested on arm64 platform but it does build on
other relevant platforms (v6.14-rc5).

Some questions:

- Is there a better method to address this problem than splitting current
  note_page() into multiple call backs as proposed here ?

- This replaces note_page(st, 0, -1, 0) with note_page_pte(st, 0, pte_zero)
  Is that problematic ? Does level = -1 has got a special meaning ? Should
  level = -1 case be handled differently possibly via a separate callback ?

Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Will Deacon <will@...nel.org>
Cc: Madhavan Srinivasan <maddy@...ux.ibm.com>
Cc: Nicholas Piggin <npiggin@...il.com>
Cc: Paul Walmsley <paul.walmsley@...ive.com>
Cc: Palmer Dabbelt <palmer@...belt.com>
Cc: Gerald Schaefer <gerald.schaefer@...ux.ibm.com>
Cc: Heiko Carstens <hca@...ux.ibm.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-arm-kernel@...ts.infradead.org
Cc: linux-kernel@...r.kernel.org
Cc: linuxppc-dev@...ts.ozlabs.org
Cc: linux-riscv@...ts.infradead.org
Cc: linux-s390@...r.kernel.org
Cc: linux-mm@...ck.org

Anshuman Khandual (2):
  mm/ptdump: Split note_page() into level specific callbacks
  arm64/ptdump: Replace u64 with pteval_t

 arch/arm64/include/asm/ptdump.h | 22 ++++++++++++-----
 arch/arm64/mm/ptdump.c          | 41 ++++++++++++++++++++++++++++---
 arch/powerpc/mm/ptdump/ptdump.c | 37 ++++++++++++++++++++++++++--
 arch/riscv/mm/ptdump.c          | 37 ++++++++++++++++++++++++++--
 arch/s390/mm/dump_pagetables.c  | 37 ++++++++++++++++++++++++++--
 arch/x86/mm/dump_pagetables.c   | 31 +++++++++++++++++++++++-
 include/linux/ptdump.h          |  7 ++++--
 mm/ptdump.c                     | 43 +++++++++++++++++++++++++--------
 8 files changed, 226 insertions(+), 29 deletions(-)

-- 
2.25.1