From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wr1-f51.google.com (mail-wr1-f51.google.com [209.85.221.51]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2E50D1DE3B7 for ; Sun, 28 Sep 2025 04:52:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.221.51 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759035139; cv=none; b=pr/5EhpbyuP4lJjjRxdQHv0UKFdeN3EzpsiqCMmRoKJvaoMpOMIlIPaSF+C7ZPy1QJmnKyCxRnLKfcK+j4GMjat83Jmv1tWnlEPJxJqJ+EspFyvT7Oid9G3Xts1r9bveRJLL1TwZG8bn56j4/0p0ObD/M2mcH0tt7e8V7wYeyo4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759035139; c=relaxed/simple; bh=V579NiAWyFA7M0hzU3TLmxji9AamGpMvr2IJYgPsK28=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=O4Ssvzien6g7ZEASkuGR4uVWqVSTFIdQbxewa5BRpJzXV83lnNIkzboiuRMYTrlz1UFS+osNDhJBKWzZKW2MEslxyD43Nr0d/gg88b12BSIz/dZRIIO5WORt9hrZ8n4hV/rrD6NYBFWMmlzzDi3Bm62kUnkpGYrkKBQ/rC1vsMs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=gmail.com; arc=none smtp.client-ip=209.85.221.51 Authentication-Results: smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Received: by mail-wr1-f51.google.com with SMTP id ffacd0b85a97d-3ee13baf2e1so2669231f8f.3 for ; Sat, 27 Sep 2025 21:52:16 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1759035135; x=1759639935; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=MDeTOOsx+C00FUGoSTYTsfkYGe7/IDMgbdTfsuLqCIw=; b=uN8W6HVU3EDqZ1/aF3C6kT36jBluCtZqPX0Cv8EDjZyR5u1Mm9VOARKf5e5J2PzUZG 9gSszvZsaknFOq6trx/wVF59KYDS9nAi/ximuLpf/fHrHL7cseESlsDsjhI3GWGmz3dN 5hVlsLJvcFCF775N1jXhrEOEYhfC3dU4qlRdUuzTIKF6OLv2J4WGUA7ny6PvPY1K4tdq ae1iRSBzE7SyOY/Alz66WTs7I28T7L4XH08nnSd7qVAGAN+iYROUoBZQtaI7bNKHXisM co0+SKiKaBO/Ysi0Je5G7wBd546eagrNiKw4+a0bkdnz1kFeO7j76MRO76SmuIFVqqWu Gg9g== X-Forwarded-Encrypted: i=1; AJvYcCV+vACmUrlTSlEi8uCveG3zHezEt8so5lHdy8og0ZIs1PMx8LfELEHwP1d5BtYWTz+yqVQEmdSjNZVz8so=@vger.kernel.org X-Gm-Message-State: AOJu0YwJ7COaT5mVxUwpAgEqXdxrzX4HccIJZE7EGNrBEpdosjgba/KE 8X9+YkJljFKV2Pa5j5fw7iiovILWDnqb1HJevrpMl0TbTWel7IQynVH5 X-Gm-Gg: ASbGncsXBBn+Oa+VDOqVHSPKApUm0ffLiDRP9eqjSgJEQFJLvjSCHT6k7dSij/nsZTB aYGE8V0o/ZDPI/xgxFF9T6AkN9raSmengTLj2CSG/YD1+nLxE4ez8fQ2UrjxL6xbW1SIjOZW9LM xqzNgc8tpryYMK/+1QzstEs0FJTszwgbkB46pfQ8E35g0YTAPGUpin0fqFkie4ssIZfkHsTh5oX e9cSVRytmNNpfmcKERetGXhaYVLcdDnNnE6aPmUnFZ3wmf9syp2HViVwfSl5mWj2WlosraJQI7l 5HlRXJ0dekupVDzuPCeA3kXqHL7H1RfG8IYZvCTh+4gWkM9aXxheP8aMZRG2KXlpRKZemMvez3b HvAwaPbfHppbz X-Google-Smtp-Source: AGHT+IHVzH6CutqdZ2xPOWXvoxdwHZpW8hcV6MdTmJ329VCEuu3lj8BtnISnCCqCDPg2So93Cnj9wg== X-Received: by 2002:a05:6000:22c2:b0:3ea:3b7b:80bb with SMTP id ffacd0b85a97d-40e4ce4c5f2mr10247690f8f.58.1759035135383; Sat, 27 Sep 2025 21:52:15 -0700 (PDT) Received: from EBJ9932692.tcent.cn ([2a09:0:1:2::302c]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-40fc5602efdsm13539465f8f.34.2025.09.27.21.52.12 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Sat, 27 Sep 2025 21:52:15 -0700 (PDT) From: Lance Yang To: akpm@linux-foundation.org, david@redhat.com Cc: xu.xin16@zte.com.cn, chengming.zhou@linux.dev, ran.xiaokai@zte.com.cn, yang.yang29@zte.com.cn, linux-kernel@vger.kernel.org, linux-mm@kvack.org, ioworker0@gmail.com, Lance Yang Subject: [PATCH 1/1] mm/ksm: fix spurious soft-dirty bit on zero-filled page merging Date: Sun, 28 Sep 2025 12:52:07 +0800 Message-ID: <20250928045207.78546-1-lance.yang@linux.dev> X-Mailer: git-send-email 2.49.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Lance Yang When KSM merges a zero-filled page with the shared zeropage, it uses pte_mkdirty() to mark the new PTE for internal accounting. However, pte_mkdirty() unconditionally sets both the hardware dirty bit and the soft-dirty bit. This behavior causes false positives in userspace tools like CRIU that rely on the soft-dirty mechanism for tracking memory changes. So, preserve the correct state by reading the old PTE under the page table lock and explicitly clearing the soft-dirty bit from the new PTE if the original was not soft-dirty. Fixes: 79271476b336 ("ksm: support unsharing KSM-placed zero pages") Signed-off-by: Lance Yang --- mm/ksm.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/mm/ksm.c b/mm/ksm.c index 04019a15b25d..e34516b8fbe4 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -1403,6 +1403,9 @@ static int replace_page(struct vm_area_struct *vma, struct page *page, * the dirty bit in zero page's PTE is set. */ newpte = pte_mkdirty(pte_mkspecial(pfn_pte(page_to_pfn(kpage), vma->vm_page_prot))); + if (!pte_soft_dirty(ptep_get(ptep))) + newpte = pte_clear_soft_dirty(newpte); + ksm_map_zero_page(mm); /* * We're replacing an anonymous page with a zero page, which is -- 2.49.0