From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 CBC1725DAEA for ; Wed, 11 Feb 2026 16:44:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770828282; cv=none; b=W/mR6ohhfU0GIBcpU+9apDqrZCL3xXW0XsYe0lVkbwG6d4iMytdFYXePp2r1OW6bdTwsdilZXxya5pqy/29sy6QUEpuOIQLUcdT563ZglqRbj5n8hfvT+XymOCugygU4oDFud5VvQSJGwA+nzA4mGv1lUrMSPIbIv70g50HJbIg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770828282; c=relaxed/simple; bh=zZDwXGHABkyfgI6f7GNhk+hSENCHTcuRnUJ7iiEY6T4=; h=Message-ID:Date:MIME-Version:Subject:From:To:Cc:References: In-Reply-To:Content-Type; b=gJCgGirqugb0LzgXt/AFtUOZd5nYIasR9eqtaygHW+9gTjKkUeWhxuOSh551vmKXU0ZPfirFyKTuJdPSiJL9CRQQoN9ugWdHshxpjGrmVp5eUSlYHGOnngYaGYuOUQ2WAbmar4h6oQm3XAjUYePgojbqG0hGOZ6/qb/znEEjrcc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=mOFAT6+9; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="mOFAT6+9" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8A6C4C19423; Wed, 11 Feb 2026 16:44:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1770828282; bh=zZDwXGHABkyfgI6f7GNhk+hSENCHTcuRnUJ7iiEY6T4=; h=Date:Subject:From:To:Cc:References:In-Reply-To:From; b=mOFAT6+9r1pqOhNwJyH+QKiM+kKmqWwbpVUCw9nACztYjI3LjrfapKAbq9v0NzYlJ 99FrmI0VZ2i5nCI2BcC8zB0serNLSjVe2w9p/DnbA+brDwxiS47HdaEj4MAEEdhzMZ ytwpHrw3OVv2lgz8LhrFq1VR7BBsnsKP0sqX/9B+VWSyYVmL2LJVfnJXyyEWPYytq1 mBa2r65CDpnCL7fFZ7f4CaFzv77qo9a9eWArS0AiRjmCY/YrDhYEE0LKh6+W+wck3X GdoBvQH0lfs0hgoMHhLAwGvLJUmBKluUvSt4yDZDf8tMuNSLMF3BRM5Eqrp8PIkR5m UjG2oXgs2WTAQ== Message-ID: <8a186f0f-c192-4e89-a11f-705c78d52233@kernel.org> Date: Wed, 11 Feb 2026 17:44:34 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: thp: Deny THP for guest_memfd and secretmem in file_thp_enabled() From: "David Hildenbrand (Arm)" To: Ackerley Tng , Deepanshu Kartikey Cc: akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, seanjc@google.com, pbonzini@redhat.com, michael.roth@amd.com, vannapurve@google.com, ziy@nvidia.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, syzbot+33a04338019ac7e43a44@syzkaller.appspotmail.com References: <20260209033558.22943-1-kartikey406@gmail.com> <0d9cada8-7148-4a5c-a09d-120ef54559d7@kernel.org> <4ed1b111-f2f1-4f89-9308-fdd9d706ca37@kernel.org> <8f188d73-fc97-414b-bdaa-e72032b2bf82@kernel.org> <5759bfba-f235-4b2d-bb30-919dcdfe7b2c@kernel.org> <3932d6b3-5de9-4c84-b60a-f2a8cc2457e2@kernel.org> Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 2/11/26 17:35, David Hildenbrand (Arm) wrote: > On 2/11/26 17:16, Ackerley Tng wrote: >> "David Hildenbrand (Arm)" writes: >> >>> >>> >>> Do you have a reproducer? If so, which behavior does it trigger? >>> >>> I would assume that we would suddenly have secretmem pages (THP) that >>> have a directmap. Or some page copy would crash the kernel. >>> >> >> Is there a good way to verify from userspace that the directmap hasn't >> been restored? Should I use CONFIG_PTDUMP_DEBUGFS? > > Anything that uses GUP must fail on that secretmem memory. Like doing an > O_DIRECT read/write or using vmsplice. > Ah, but that might still fail, because we can identify the page as such. Hm ... we'd need some introspection interface indeed. -- Cheers, David