From: Yeoreum Yun <yeoreum.yun@arm.com>
To: Russell King <linux@armlinux.org.uk>,
Huacai Chen <chenhuacai@kernel.org>,
WANG Xuerui <kernel@xen0n.name>,
Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
Andrew Morton <akpm@linux-foundation.org>,
Kairui Song <kasong@tencent.com>, Qi Zheng <qi.zheng@linux.dev>,
Shakeel Butt <shakeel.butt@linux.dev>,
Barry Song <baohua@kernel.org>,
Axel Rasmussen <axelrasmussen@google.com>,
Yuanchu Xie <yuanchu@google.com>, Wei Xu <weixugc@google.com>,
Johannes Weiner <hannes@cmpxchg.org>,
David Hildenbrand <david@kernel.org>,
Michal Hocko <mhocko@kernel.org>,
Lorenzo Stoakes <ljs@kernel.org>,
Tianrui Zhao <zhaotianrui@loongson.cn>,
Bibo Mao <maobibo@loongson.cn>, Anup Patel <anup@brainfault.org>,
Atish Patra <atish.patra@linux.dev>,
Paul Walmsley <pjw@kernel.org>,
Palmer Dabbelt <palmer@dabbelt.com>,
Albert Ou <aou@eecs.berkeley.edu>,
Alexandre Ghiti <alex@ghiti.fr>,
Dave Hansen <dave.hansen@linux.intel.com>,
Andy Lutomirski <luto@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@kernel.org>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
"Liam R. Howlett" <liam@infradead.org>,
Vlastimil Babka <vbabka@kernel.org>,
Mike Rapoport <rppt@kernel.org>,
Suren Baghdasaryan <surenb@google.com>,
Michal Hocko <mhocko@suse.com>, Jonas Bonn <jonas@southpole.se>,
Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>,
Stafford Horne <shorne@gmail.com>
Cc: linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, loongarch@lists.linux.dev,
linux-mips@vger.kernel.org, linux-arch@vger.kernel.org,
linux-mm@kvack.org, kvm@vger.kernel.org,
kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org,
linux-openrisc@vger.kernel.org,
Yeoreum Yun <yeoreum.yun@arm.com>
Subject: [PATCH RFC v3 19/21] mm/pgtable: disallow calling (pgd|p4d|pud)_page, pgd_page_vaddr() and (p4d|pud)_pgtable with dummy
Date: Wed, 02 Sep 2026 12:56:21 +0100 [thread overview]
Message-ID: <20260902-dummy_ptxp3-v3-19-5d8f5b17c25c@arm.com> (raw)
In-Reply-To: <20260902-dummy_ptxp3-v3-0-5d8f5b17c25c@arm.com>
From: "David Hildenbrand (Arm)" <david@kernel.org>
These helpers silently fallback to the folded helpers. With e.g., pdgp_get()
returning dummy values, pgd_page_vaddr(pgdp_get(pgdp)) will now behave
differently than pgd_page_vaddr(*pgdp).
Disallow calling (pgd|p4d|pud)_page() entirely, and catch when passing a
dummy value to pgd_page_vaddr() and (p4d|pud)_pgtable.
This will catch most abuse of dummy pXdp value at compile time --
so far there were none, and it better stay that way.
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
Co-developed-by: Yeoreum Yun <yeoreum.yun@arm.com>
Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
---
include/asm-generic/pgtable-nop4d.h | 8 ++++++--
include/asm-generic/pgtable-nopmd.h | 8 ++++++--
include/asm-generic/pgtable-nopud.h | 8 ++++++--
3 files changed, 18 insertions(+), 6 deletions(-)
diff --git a/include/asm-generic/pgtable-nop4d.h b/include/asm-generic/pgtable-nop4d.h
index 2d86325235da..d2dccf7542da 100644
--- a/include/asm-generic/pgtable-nop4d.h
+++ b/include/asm-generic/pgtable-nop4d.h
@@ -70,8 +70,12 @@ static __always_inline p4d_t *__p4d_offset_lockless(pgd_t *pgdp, pgd_t pgd,
#define p4d_val(x) (pgd_val((x).pgd))
#define __p4d(x) ((p4d_t) { __pgd(x) })
-#define pgd_page(pgd) (p4d_page((p4d_t){ pgd }))
-#define pgd_page_vaddr(pgd) ((unsigned long)(p4d_pgtable((p4d_t){ pgd })))
+#define pgd_page(pgd) ({ BUILD_BUG(); (struct page *)NULL; })
+#define pgd_page_vaddr(pgd) \
+({ \
+ pgd_check_dummy(pgd); \
+ (unsigned long)p4d_pgtable((p4d_t) { pgd }); \
+})
/*
* allocating and freeing a p4d is trivial: the 1-entry p4d is
diff --git a/include/asm-generic/pgtable-nopmd.h b/include/asm-generic/pgtable-nopmd.h
index bd40d3a5743f..2afbf2d8659d 100644
--- a/include/asm-generic/pgtable-nopmd.h
+++ b/include/asm-generic/pgtable-nopmd.h
@@ -79,8 +79,12 @@ static __always_inline pmd_t *__pmd_offset_lockless(pud_t *pudp, pud_t pud,
#define pmd_val(x) (pud_val((x).pud))
#define __pmd(x) ((pmd_t) { __pud(x) } )
-#define pud_page(pud) (pmd_page((pmd_t){ pud }))
-#define pud_pgtable(pud) ((pmd_t *)(pmd_page_vaddr((pmd_t){ pud })))
+#define pud_page(pud) ({ BUILD_BUG(); (struct page *)NULL; })
+#define pud_pgtable(pud) \
+({ \
+ pud_check_dummy(pud); \
+ ((pmd_t *)(pmd_page_vaddr((pmd_t) { pud }))); \
+})
/*
* allocating and freeing a pmd is trivial: the 1-entry pmd is
diff --git a/include/asm-generic/pgtable-nopud.h b/include/asm-generic/pgtable-nopud.h
index 7475d0bd0f2e..3264673c0c38 100644
--- a/include/asm-generic/pgtable-nopud.h
+++ b/include/asm-generic/pgtable-nopud.h
@@ -77,8 +77,12 @@ static __always_inline pud_t *__pud_offset_lockless(p4d_t *p4dp, p4d_t p4d,
#define pud_val(x) (p4d_val((x).p4d))
#define __pud(x) ((pud_t) { __p4d(x) })
-#define p4d_page(p4d) (pud_page((pud_t){ p4d }))
-#define p4d_pgtable(p4d) ((pud_t *)(pud_pgtable((pud_t){ p4d })))
+#define p4d_page(p4d) ({ BUILD_BUG(); (struct page *)NULL; })
+#define p4d_pgtable(p4d) \
+({ \
+ p4d_check_dummy(p4d); \
+ ((pud_t *)(pud_pgtable((pud_t) { p4d }))); \
+})
/*
* allocating and freeing a pud is trivial: the 1-entry pud is
--
2.43.0
next prev parent reply other threads:[~2026-09-02 11:59 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-02 11:56 [PATCH RFC v3 00/21] mm: change behavior of pXdp_get()/pXd_page() in compile-time folded pgtable Yeoreum Yun
2026-09-02 11:56 ` [PATCH RFC v3 01/21] ARM: mm: make nommu pgd_t a scalar Yeoreum Yun
2026-09-02 11:56 ` [PATCH RFC v3 02/21] ARM: mm: make 2-level " Yeoreum Yun
2026-09-02 11:56 ` [PATCH RFC v3 03/21] ARM: mm: remove custom pgdp_get() Yeoreum Yun
2026-09-02 11:56 ` [PATCH RFC v3 04/21] LoongArch: mm: define pud_leaf() only when PUD exists Yeoreum Yun
2026-09-02 11:56 ` [PATCH RFC v3 05/21] MIPS: " Yeoreum Yun
2026-09-02 11:56 ` [PATCH RFC v3 06/21] mm/pgtable: define (pgd|p4d|pud)_leaf() for folded page tables Yeoreum Yun
2026-09-02 12:15 ` sashiko-bot
2026-09-02 11:56 ` [PATCH RFC v3 07/21] mm/pgtable: define (pgd|p4d|pud)_offset_lockless() " Yeoreum Yun
2026-09-02 11:56 ` [PATCH RFC v3 08/21] mm: vmscan: remove stack copy address of pud/pmd pass in walk_pud/pmd_range() Yeoreum Yun
2026-09-02 11:56 ` [PATCH RFC v3 09/21] loongarch: kvm: remove stack copy address of pXd in pXd_offset() Yeoreum Yun
2026-09-02 12:19 ` sashiko-bot
2026-09-02 12:38 ` Yeoreum Yun
2026-09-02 11:56 ` [PATCH RFC v3 10/21] riscv: " Yeoreum Yun
2026-09-02 11:56 ` [PATCH RFC v3 11/21] riscv: mm: use proper set_pXd() for generic compile-time folded patable in vmalloc_fault() Yeoreum Yun
2026-09-02 11:56 ` [PATCH RFC v3 12/21] mm/pgtable: redefine PGTABLE_LEVEL enum with ascend order from PGD Yeoreum Yun
2026-09-02 11:56 ` [PATCH RFC v3 13/21] x86: mm: use pgtable_level enum in effective_prot_pXd() Yeoreum Yun
2026-09-02 20:48 ` Dave Hansen
2026-09-02 11:56 ` [PATCH RFC v3 14/21] x86: mm: carve out the generic compile-time folded pgtable case in effective_prot() Yeoreum Yun
2026-09-02 20:46 ` Dave Hansen
2026-09-02 11:56 ` [PATCH RFC v3 15/21] x86: mm: skip collapse_pud_page() when CONFIG_X86_DIRECT_GBPAGES disabled Yeoreum Yun
2026-09-02 12:17 ` sashiko-bot
2026-09-02 12:29 ` Yeoreum Yun
2026-09-02 15:38 ` Dave Hansen
2026-09-02 16:48 ` Yeoreum Yun
2026-09-02 11:56 ` [PATCH RFC v3 16/21] openrisc/pgtable: drop __pmd_offset() Yeoreum Yun
2026-09-02 11:56 ` [PATCH RFC v3 17/21] mm/pgtable: optimize pmdp_get() and friends for folded pagetable levels Yeoreum Yun
2026-09-02 11:56 ` [PATCH RFC v3 18/21] mm/pgtable: catch abuse of folded dummy pgd_t/p4d_t/pud_t Yeoreum Yun
2026-09-02 11:56 ` Yeoreum Yun [this message]
2026-09-02 11:56 ` [PATCH RFC v3 20/21] mm/pgtable: disallow calling folded set_pgd/set_p4d/set_pud with dummy Yeoreum Yun
2026-09-02 11:56 ` [PATCH RFC v3 21/21] Documentation: mm: clarify behaviour of compile-time folded page tables Yeoreum Yun
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