From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2910C3403FF for ; Wed, 9 Sep 2026 09:46:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788947215; cv=none; b=sKOJwAnDFOKfCUXHBTY7hW/7P1vCK6yKl+2EhJM6cIF/dma4805WURVCSQ9fz80XLa3vvMYrNuKIw8mv95JCY2qDvRKejFw4JcPS7mKUecHyBg6TWc5pPF6O/xKr0Tz6voKrM+Z0rGvEEqHtomxNFLLSYEO39VkhI3XUPeI5XcE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788947215; c=relaxed/simple; bh=UuqonKx0I3am9CHzEdWIFg149idU28s0NzFvvellkLU=; h=Subject:To:Cc:From:Date:Message-ID:MIME-Version:Content-Type; b=hcK/YddJVK+KXnHQiqRu3kpEPDxWlE80SDFloqoGtciHiMncUB+7IOv9SWALasLkV5FANMAOiPx+/la6Wz056aZ6r+0MoL8XXIgjNYGxS16bN8/y8F70dAix6jxluneNqOt4p+c0Bi9vnb0JE3deYtIotSJ7t+U08HiWqG34ynk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=BDkBcdsQ; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="BDkBcdsQ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7FE3B1F00A3F; Wed, 9 Sep 2026 09:46:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1788947214; bh=Jh5MHSqz/VfE3alIzEqrCzFQih0r866w83KgMeFplC0=; h=Subject:To:Cc:From:Date; b=BDkBcdsQBV4zJM8EyuaaZlvnqWnDm7/A9GC+h/dbL3kMGkEtsDHwKn1gBmxDHYK5F XMIYSoTAi4dPdI0OdI1z+3AKeEmQu2y9hWFOohEE4dh1jl+aAfM1DPJPB+cGViSxbE 9VDbhBB0OP08XoEiKmK41LvVrIroePlGBL2lXUck= Subject: FAILED: patch "[PATCH] arm64: mm: Fix the lockless page-table walk in show_pte()" failed to apply to 5.15-stable tree To: kmehltretter@gmail.com,will@kernel.org Cc: From: Date: Wed, 09 Sep 2026 11:41:41 +0200 Message-ID: <2026090941-average-edition-4184@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit The patch below does not apply to the 5.15-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y git checkout FETCH_HEAD git cherry-pick -x a77644d009dece1104b6fcc6e322b0e4503db0d6 # git commit -s git send-email --to '' --in-reply-to '2026090941-average-edition-4184@gregkh' --subject-prefix 'PATCH 5.15.y' 'HEAD^..' Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From a77644d009dece1104b6fcc6e322b0e4503db0d6 Mon Sep 17 00:00:00 2001 From: Karl Mehltretter Date: Fri, 28 Aug 2026 19:41:31 +0200 Subject: [PATCH] arm64: mm: Fix the lockless page-table walk in show_pte() show_pte() walks page tables locklessly and can run with interrupts enabled. A concurrent teardown can free a table page while it is being walked. It can also clear a parent entry after show_pte() checked it; the regular pXd_offset() helpers then reread the cleared entry and can derive a bogus lower-level pointer and fault again. Use the lockless offset helpers with the saved parent entries, as gup_fast() does, and pass the saved PMD to pte_offset_map(). For task page tables, arm64 selects MMU_GATHER_RCU_TABLE_FREE. Disable local interrupts around the walk to hold off RCU-deferred table frees and block the tlb_remove_table_sync_one() IPI until the walk is finished. Place the IRQ guard after the header print. This does not make the output a consistent snapshot, but prevents the task page-table walk from dereferencing a released table page or deriving a pointer from a different parent value. Fixes: 1d18c47c735e ("arm64: MMU fault handling and page table management") Cc: stable@vger.kernel.org Assisted-by: LLM Signed-off-by: Karl Mehltretter Signed-off-by: Will Deacon diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c index 0b52557652be..75c3e463df2e 100644 --- a/arch/arm64/mm/fault.c +++ b/arch/arm64/mm/fault.c @@ -16,6 +16,7 @@ #include #include #include +#include #include #include #include @@ -154,6 +155,9 @@ static void show_pte(unsigned long addr) pr_alert("%s pgtable: %luk pages, %llu-bit VAs, pgdp=%016lx\n", mm == &init_mm ? "swapper" : "user", PAGE_SIZE / SZ_1K, vabits_actual, mm_to_pgd_phys(mm)); + + guard(irqsave)(); + pgdp = pgd_offset(mm, addr); pgd = READ_ONCE(*pgdp); pr_alert("[%016lx] pgd=%016llx", addr, pgd_val(pgd)); @@ -167,25 +171,25 @@ static void show_pte(unsigned long addr) if (pgd_none(pgd) || pgd_bad(pgd)) break; - p4dp = p4d_offset(pgdp, addr); + p4dp = p4d_offset_lockless(pgdp, pgd, addr); p4d = READ_ONCE(*p4dp); pr_cont(", p4d=%016llx", p4d_val(p4d)); if (p4d_none(p4d) || p4d_bad(p4d)) break; - pudp = pud_offset(p4dp, addr); + pudp = pud_offset_lockless(p4dp, p4d, addr); pud = READ_ONCE(*pudp); pr_cont(", pud=%016llx", pud_val(pud)); if (pud_none(pud) || pud_bad(pud)) break; - pmdp = pmd_offset(pudp, addr); + pmdp = pmd_offset_lockless(pudp, pud, addr); pmd = READ_ONCE(*pmdp); pr_cont(", pmd=%016llx", pmd_val(pmd)); if (pmd_none(pmd) || pmd_bad(pmd)) break; - ptep = pte_offset_map(pmdp, addr); + ptep = pte_offset_map(&pmd, addr); if (!ptep) break;