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smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=QiSloQfr; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 77CF460A2609; Mon, 26 Oct 2026 09:41:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=QiSloQfr Received: by smtp.kernel.org (Postfix) with ESMTPSA id D665E1F01829; Mon, 26 Oct 2026 09:41:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793007672; bh=REIzglI+UokdSSqST5CDOezePfcdiVtDX4vr1iybjIw=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=QiSloQfro7y48xGi4gcFNCghKwpJoJ0tKGbEHTBRyyphetxebruHsVADA4ArSYXur 8hVsrDaMZUzgAXNsEMae6m8qD0JSY0GeC9mYZUYW3HBpFztHdb0544QYlbPpTVaWzz 7YBcsNT66LipxPoZ6bopJ4Pqe7irxDLQa6Eq96Wu1HSvlTlrWu1hy4ZackBV5OnSf6 KprOyE0ZVhA0yNVB5Sf8yMQwprTqDaGr5QY56YIcRQXyBpcIBhbRXjjW6aG03+v3Vl 4TcpefDK8jjvxK8uoAnrWkCx+40PxsMvF6jOFIiLFWiYcSz5nnu/hIm1g3ecCB/m8G 2thglL7zp4u8g== Message-ID: Date: Sun, 25 Oct 2026 13:36:27 +0100 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] mm/ksm: keep soft-dirty when merging a page To: Samarth Narang , Andrew Morton Cc: Xu Xin , Chengming Zhou , Peter Xu , Kiryl Shutsemau , Mike Rapoport , Lance Yang , linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20261021182157.1873726-1-samarth.colleges@gmail.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/21/26 20:21, Samarth Narang wrote: > replace_page() maps the KSM page with a PTE built from scratch, so the > soft-dirty bit of the PTE it replaces is lost. A page written since > "clear_refs 4" then no longer shows as soft-dirty once it is merged, and > a soft-dirty based dumper treats it as unchanged. > > Copy the soft-dirty bit from the original PTE to the new PTE. > > Fixes: 0f8975ec4db2 ("mm: soft-dirty bits for user memory changes tracking") > Cc: stable@vger.kernel.org > Assisted-by: LLM > Signed-off-by: Samarth Narang > --- > > Notes: > v2: https://lore.kernel.org/all/20261019010934.697895-1-samarth.colleges@gmail.com/ > > Changes since v2: > - Keep only the soft-dirty fix, as David suggested; Lance will be handling > the uffd-wp/RWP part. > - Fixes tag reduced to the soft-dirty commit. > - Dropped the Tested-by tag, since the patch changed. > > mm/ksm.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/mm/ksm.c b/mm/ksm.c > index dbfb8f98b189..910a1307ac9f 100644 > --- a/mm/ksm.c > +++ b/mm/ksm.c > @@ -1463,6 +1463,10 @@ static int replace_page(struct vm_area_struct *vma, struct page *page, > dec_mm_counter(mm, MM_ANONPAGES); > } > > + /* Preserve soft-dirty when replacing the page. */ > + if (pte_soft_dirty(orig_pte)) > + newpte = pte_mksoft_dirty(newpte); > + Acked-by: David Hildenbrand (Arm) -- Cheers, David