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 C9EA5257824 for ; Wed, 12 Nov 2025 08:05:11 +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=1762934711; cv=none; b=PYI5z1WDvDWSqb2S6s4lJ5Gwv7/9NOzcZsL6yisw1thF2OwTgRC8T5nzYsPjWtnDc0ELM8LcvSdN/uPsLEsoePtyv+B7b4C69ybDM++QU1AIshCQBvRmkUd8YcAoS0WWAqeDhxhvxdai/muX0NZsPcpF6iXQFXf1FP32RtGZtC0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762934711; c=relaxed/simple; bh=SA7i33ysWzPDlrhtd68Z/egkmmkPzs0rHOKGyx4PbTY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ZLsD3qSZy6e6FIa0dIj8UeC1U7JKhAVLRp9Wi+ttWEw1MYJiHLURCXtdi4tysRWAl2k8r6PFbhfx+7NFySAxLQ35oWe4pMjuv6ySLdG4ZqUOq37WIvqMyaujFNssd7oIzoByxMzG+m2kuAWdJt0DUInDXLoej3EqqMvXGe7K7BM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=KdQrzR3v; 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="KdQrzR3v" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 89486C16AAE; Wed, 12 Nov 2025 08:05:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1762934711; bh=SA7i33ysWzPDlrhtd68Z/egkmmkPzs0rHOKGyx4PbTY=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=KdQrzR3vf+z1dXt8moVE4lWL0xR6YvwRPceeAI609o8bZcg0tfarInopUZdeROePM MzbHN7CuSrgHjf2d6E3N34UssO7AdaZLpXc8x8qV6la0CuoHkV7BzW0wYqy9vWsEnN zqrejZxeQWsmg03EZUrEmhytog3MWalbPNdPhzfB1sCQxBENXv1srgxqZQCWyq+gGd r/pL0Dvss93HZcQ0j/doy+dMk09NmRk76+wCr1wofTRm5EPDthGgzViu61q2QtSpms cbCmjww2cTrehhj0y7cvy1PYaAD88KbMJc1mMg61gXLcdtgzfpTs9XXtytuFksal/V U26qPyjAo2dzQ== Message-ID: <7b78c1d8-9efc-4570-8f4c-244af665a159@kernel.org> Date: Wed, 12 Nov 2025 09:05:07 +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/gup: fix handling of zero page in follow_page_pte() To: peng8420.li@gmail.com, linux-mm@kvack.org, akpm@linux-foundation.org Cc: osalvador@suse.de, jgg@ziepe.ca, jhubbard@nvidia.com, peterx@redhat.com, linux-kernel@vger.kernel.org, dan.j.williams@intel.com References: <20251112072424.125514-1-peng8420.li@gmail.com> From: "David Hildenbrand (Red Hat)" Content-Language: en-US In-Reply-To: <20251112072424.125514-1-peng8420.li@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 12.11.25 08:24, peng8420.li@gmail.com wrote: > From: "peng8420.li" > > In some scenarios, `__vm_normal_page` might return NULL. > In this case, if `is_zero_pfn(pte_pfn(pte))` is true, simply return `page = pte_page(pte)`; > no further folio processing is needed. > > Signed-off-by: peng8420.li > --- > mm/gup.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/mm/gup.c b/mm/gup.c > index 95d948c8e86c..60ae5f0c20e0 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -838,6 +838,7 @@ static struct page *follow_page_pte(struct vm_area_struct *vma, > > if (is_zero_pfn(pte_pfn(pte))) { > page = pte_page(pte); > + goto out; > } else { > ret = follow_pfn_pte(vma, address, ptep, flags); > page = ERR_PTR(ret); I'm sorry, but that's just wrong. Observe how me might run into the gup_must_unshare() branch and how try_grab_folio() would grab references on the FOLL_GET path. -- Cheers David