From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 046544BF939 for ; Tue, 22 Sep 2026 06:16:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790057817; cv=none; b=VwEGk4S7BG8kVtW2BIFejMen2qb8M/jOx78hfxilTUOGzotJId7jEshQbgEKax1TJi7eb7KzJJ3o1xcKVsRPzL9tgbgqiiKl9SW0vZt4vFLOY6aG3wvaomyUfkFMC8PL9QLu4ytoAy1PfgtreBAZk23cLpXS3TNYZ/UKxK34coA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790057817; c=relaxed/simple; bh=MpnntGHJ8hu3lzncZnuAewJpmhM2iJ+Ei03Xl4MTGF8=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=dqK71h5EcpYOIiaF4JIo3JG/+VJYKk3uhOML1KCCqEv4sqPxsKY+/fqh3/ATPxWJm4+5AFXN+D0+Lnx+EvFdE2eSGcp8JqFWLG7OwQPBRZYhbaVl+hDa+zNECVj15g6I5pjb52U7XjuAyiWoPP3h0yTy4o0/abSLvdzcjOG7los= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=bf29M5Gv; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="bf29M5Gv" Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id D1DB4152B; Mon, 21 Sep 2026 23:16:51 -0700 (PDT) Received: from localhost (a085714.arm.com [10.164.19.28]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 9F81E3F632; Mon, 21 Sep 2026 23:16:54 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1790057815; bh=MpnntGHJ8hu3lzncZnuAewJpmhM2iJ+Ei03Xl4MTGF8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=bf29M5GvjhPa+GXFpLah+FqNO9adCknuWuj7gh6DWF3CdMKtV6K6W7uzCfTThPuyf o8sfPSxEtlIUezX0Zi0+ZvqwPDUwIhIYiYhXYNOS7X2oieTub00Jofeg0p+zeEEaoc uZv4pSO9QRu+iMo3Y54vBM4l+fxijgjrkQZ9cD2I= 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 V2 3/4] arm64/mm: Use p4dp_get() for P4D accesses Date: Tue, 22 Sep 2026 11:46:37 +0530 Message-ID: <20260922061638.3967467-4-anshuman.khandual@arm.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260922061638.3967467-1-anshuman.khandual@arm.com> References: <20260922061638.3967467-1-anshuman.khandual@arm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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. 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 --- 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 ++-- 7 files changed, 14 insertions(+), 14 deletions(-) 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