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h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=OPa+4zC9f9wtpdd0jHUw79KM+PmDxqo33Qy51Nr+CSk2x54pJbO4UOQECBNk17oDq 47MeSSMtXam3UGJyZu6M9VB3iRorzwxWRsq7g8W5HqFQbtmH5CdE98QL3hJFujMxol IgHW3ux46V5woHgSfjyTUXHAUC4ccX0FKBiX3G6Q= From: Anshuman Khandual To: linux-arm-kernel@lists.infradead.org Cc: Anshuman Khandual , Catalin Marinas , Will Deacon , Ryan Roberts , Mark Rutland , Lorenzo Stoakes , Andrew Morton , David Hildenbrand , Mike Rapoport , Linu Cherian , linux-kernel@vger.kernel.org, linux-mm@kvack.org, kasan-dev@googlegroups.com Subject: [PATCH V3 3/4] arm64/mm: Use p4dp_get() for P4D accesses Date: Thu, 24 Sep 2026 11:52:13 +0530 Message-ID: <20260924062214.1635078-4-anshuman.khandual@arm.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260924062214.1635078-1-anshuman.khandual@arm.com> References: <20260924062214.1635078-1-anshuman.khandual@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: C456820004 X-Rspam-User: X-Stat-Signature: 4tcfow3mfa17hpftow8mnzx97f95duk4 X-HE-Tag: 1790230954-737165 X-HE-Meta: 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 3xNkn0cu SZoRXva6a3hykvk5MTJ9m0c1VxXWdpK0bQ6yAIodeuOIKT92Lzsbh4ouMJIIGG08/xhSTfRXR5xAM9jz5E2Wo32OqZFdMnl/ofeUcvZPkwbv4lbv1AO9iD81Gvu+maHFUC6dAdMmpUkdnA7E2niX6bR70vsLFrAh6Ej80sE8E0+JB0M080gy73BeA9oqouI6SwQyb5qy4hILust+geY8uBWafivhsy90kA85ZrN8FIHMeSJEBs3MHzIZ8PW0fL1RPmJozsNLoVJgDwBTKr7tDkW56/Rbc9eG3nXY0C8Xl4+2vA7qbMK97K+KSzJlogRLY/1Dr7WYGVQFufiKWmQyyi8bxBIOxojlrnK5FKqLJWRIUvJNvQttQGaIHO2mDNgCMUpHAXCivC3RSfSh1FQLHekq0ehFiUoV5/o3lZ8S/gd1L3R1AmlazCrCcKk5RmA09IuJQpMGsHQL8+1TsYb+fZmhBHmJkSCoYAx5nELpJE0mDdPc= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Replace READ_ONCE() with p4dp_get() for P4D accesses in preparation for supporting both D64 and D128 translation table formats. READ_ONCE() cannot currently be used for 128-bit page table entries on arm64 because it does not provide the required 128-bit single-copy atomicity, causing builds to fail for accesses wider than 64 bits. Although LDP/STP provide the required atomicity when FEAT_LSE is available (as required by FEAT_D128), extending READ_ONCE() to support 128-bit accesses is undesirable. READ_ONCE() is a general-purpose API, so doing so could encourage other 128-bit users that would either fail to build in configurations without D128 support or, if D128 becomes a runtime option, silently permit tearing on systems without the required hardware support. Instead, standardize P4D accesses on the existing page-table helpers. These can be overridden on arm64 to provide 128-bit single-copy atomicity when required. For now override p4dp_get() which is same as the generic memory default to avoid build dependency problem for callers in header . No functional change intended. Cc: Catalin Marinas Cc: Will Deacon Cc: Ryan Roberts Cc: Mark Rutland Cc: linux-arm-kernel@lists.infradead.org Cc: linux-kernel@vger.kernel.org Cc: kasan-dev@googlegroups.com Signed-off-by: Anshuman Khandual --- Changes in V3 - Added platform override for p4dp_get() - Replaced READ_ONCE() in pud_offset_phys() and pud_offset() arch/arm64/include/asm/pgtable.h | 10 ++++++++-- arch/arm64/mm/fault.c | 2 +- arch/arm64/mm/fixmap.c | 2 +- arch/arm64/mm/hugetlbpage.c | 2 +- arch/arm64/mm/kasan_init.c | 4 ++-- arch/arm64/mm/mmu.c | 12 ++++++------ arch/arm64/mm/pageattr.c | 2 +- arch/arm64/mm/trans_pgd.c | 4 ++-- 8 files changed, 22 insertions(+), 16 deletions(-) diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h index b46930f844a2..f235f68a7518 100644 --- a/arch/arm64/include/asm/pgtable.h +++ b/arch/arm64/include/asm/pgtable.h @@ -96,6 +96,12 @@ static inline pud_t pudp_get(pud_t *pudp) return READ_ONCE(*pudp); } +#define p4dp_get p4dp_get +static inline p4d_t p4dp_get(p4d_t *p4dp) +{ + return READ_ONCE(*p4dp); +} + #ifdef CONFIG_TRANSPARENT_HUGEPAGE #define __HAVE_ARCH_FLUSH_PMD_TLB_RANGE @@ -976,7 +982,7 @@ static inline phys_addr_t pud_offset_phys(p4d_t *p4dp, unsigned long addr) { VM_WARN_ON_ONCE(!pgtable_l4_enabled()); - return p4d_page_paddr(READ_ONCE(*p4dp)) + pud_index(addr) * sizeof(pud_t); + return p4d_page_paddr(p4dp_get(p4dp)) + pud_index(addr) * sizeof(pud_t); } static inline @@ -990,7 +996,7 @@ pud_t *pud_offset_lockless(p4d_t *p4dp, p4d_t p4d, unsigned long addr) static inline pud_t *pud_offset(p4d_t *p4dp, unsigned long addr) { - return pud_offset_lockless(p4dp, READ_ONCE(*p4dp), addr); + return pud_offset_lockless(p4dp, p4dp_get(p4dp), addr); } #define pud_offset pud_offset diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c index 435e2e14c070..a6afd8929a10 100644 --- a/arch/arm64/mm/fault.c +++ b/arch/arm64/mm/fault.c @@ -174,7 +174,7 @@ static void show_pte(unsigned long addr) break; p4dp = p4d_offset_lockless(pgdp, pgd, addr); - p4d = READ_ONCE(*p4dp); + p4d = p4dp_get(p4dp); ptval_to_str(pxd_str, p4d_val(p4d)); pr_cont(", p4d=%s", pxd_str); if (p4d_none(p4d) || p4d_bad(p4d)) diff --git a/arch/arm64/mm/fixmap.c b/arch/arm64/mm/fixmap.c index d9a870836faf..2a0fe0b0f771 100644 --- a/arch/arm64/mm/fixmap.c +++ b/arch/arm64/mm/fixmap.c @@ -74,7 +74,7 @@ static void __init early_fixmap_init_pmd(pud_t *pudp, unsigned long addr, static void __init early_fixmap_init_pud(p4d_t *p4dp, unsigned long addr, unsigned long end) { - p4d_t p4d = READ_ONCE(*p4dp); + p4d_t p4d = p4dp_get(p4dp); pud_t *pudp; if (CONFIG_PGTABLE_LEVELS > 3 && !p4d_none(p4d) && diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c index c9ad5e75b073..5771bf49e1fe 100644 --- a/arch/arm64/mm/hugetlbpage.c +++ b/arch/arm64/mm/hugetlbpage.c @@ -288,7 +288,7 @@ pte_t *huge_pte_offset(struct mm_struct *mm, return NULL; p4dp = p4d_offset(pgdp, addr); - if (!p4d_present(READ_ONCE(*p4dp))) + if (!p4d_present(p4dp_get(p4dp))) return NULL; pudp = pud_offset(p4dp, addr); diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c index aad29bcc7622..4dd8c1186471 100644 --- a/arch/arm64/mm/kasan_init.c +++ b/arch/arm64/mm/kasan_init.c @@ -89,7 +89,7 @@ static pmd_t *__init kasan_pmd_offset(pud_t *pudp, unsigned long addr, int node, static pud_t *__init kasan_pud_offset(p4d_t *p4dp, unsigned long addr, int node, bool early) { - if (p4d_none(READ_ONCE(*p4dp))) { + if (p4d_none(p4dp_get(p4dp))) { phys_addr_t pud_phys = early ? __pa_symbol(kasan_early_shadow_pud) : kasan_alloc_zeroed_page(node); @@ -162,7 +162,7 @@ static void __init kasan_p4d_populate(pgd_t *pgdp, unsigned long addr, do { next = p4d_addr_end(addr, end); kasan_pud_populate(p4dp, addr, next, node, early); - } while (p4dp++, addr = next, addr != end && p4d_none(READ_ONCE(*p4dp))); + } while (p4dp++, addr = next, addr != end && p4d_none(p4dp_get(p4dp))); } static void __init kasan_pgd_populate(unsigned long addr, unsigned long end, diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c index 22efaee79293..83709d987e7c 100644 --- a/arch/arm64/mm/mmu.c +++ b/arch/arm64/mm/mmu.c @@ -367,7 +367,7 @@ static int alloc_init_pud(p4d_t *p4dp, unsigned long addr, unsigned long end, { int ret = 0; unsigned long next; - p4d_t p4d = READ_ONCE(*p4dp); + p4d_t p4d = p4dp_get(p4dp); pud_t *pudp; if (p4d_none(p4d)) { @@ -457,7 +457,7 @@ static int alloc_init_p4d(pgd_t *pgdp, unsigned long addr, unsigned long end, } do { - p4d_t old_p4d = READ_ONCE(*p4dp); + p4d_t old_p4d = p4dp_get(p4dp); next = p4d_addr_end(addr, end); @@ -467,7 +467,7 @@ static int alloc_init_p4d(pgd_t *pgdp, unsigned long addr, unsigned long end, goto out; VM_WARN_ON_ONCE(p4d_val(old_p4d) != 0 && - p4d_val(old_p4d) != READ_ONCE(p4d_val(*p4dp))); + p4d_val(old_p4d) != (p4d_val(p4dp_get(p4dp)))); phys += next - addr; } while (p4dp++, addr = next, addr != end); @@ -1622,7 +1622,7 @@ static void unmap_hotplug_p4d_range(pgd_t *pgdp, unsigned long addr, do { next = p4d_addr_end(addr, end); p4dp = p4d_offset(pgdp, addr); - p4d = READ_ONCE(*p4dp); + p4d = p4dp_get(p4dp); if (p4d_none(p4d)) continue; @@ -1788,7 +1788,7 @@ static void free_empty_p4d_table(pgd_t *pgdp, unsigned long addr, do { next = p4d_addr_end(addr, end); p4dp = p4d_offset(pgdp, addr); - p4d = READ_ONCE(*p4dp); + p4d = p4dp_get(p4dp); if (p4d_none(p4d)) continue; @@ -1809,7 +1809,7 @@ static void free_empty_p4d_table(pgd_t *pgdp, unsigned long addr, */ p4dp = p4d_offset(pgdp, 0UL); for (i = 0; i < PTRS_PER_P4D; i++) { - if (!p4d_none(READ_ONCE(p4dp[i]))) + if (!p4d_none(p4dp_get(p4dp + i))) return; } diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c index 07b2fa4de57f..826856ef64a8 100644 --- a/arch/arm64/mm/pageattr.c +++ b/arch/arm64/mm/pageattr.c @@ -403,7 +403,7 @@ bool kernel_page_present(struct page *page) return false; p4dp = p4d_offset(pgdp, addr); - if (p4d_none(READ_ONCE(*p4dp))) + if (p4d_none(p4dp_get(p4dp))) return false; pudp = pud_offset(p4dp, addr); diff --git a/arch/arm64/mm/trans_pgd.c b/arch/arm64/mm/trans_pgd.c index d119119455f1..7afe2beca4ba 100644 --- a/arch/arm64/mm/trans_pgd.c +++ b/arch/arm64/mm/trans_pgd.c @@ -99,7 +99,7 @@ static int copy_pud(struct trans_pgd_info *info, p4d_t *dst_p4dp, unsigned long next; unsigned long addr = start; - if (p4d_none(READ_ONCE(*dst_p4dp))) { + if (p4d_none(p4dp_get(dst_p4dp))) { dst_pudp = trans_alloc(info); if (!dst_pudp) return -ENOMEM; @@ -145,7 +145,7 @@ static int copy_p4d(struct trans_pgd_info *info, pgd_t *dst_pgdp, src_p4dp = p4d_offset(src_pgdp, start); do { next = p4d_addr_end(addr, end); - if (p4d_none(READ_ONCE(*src_p4dp))) + if (p4d_none(p4dp_get(src_p4dp))) continue; if (copy_pud(info, dst_p4dp, src_p4dp, addr, next)) return -ENOMEM; -- 2.43.0