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 840B2282F04; Mon, 20 Apr 2026 19:29:49 +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=1776713389; cv=none; b=X3Quhkuf5yzcA5zMc/ZHV3tQcHqFe+fk1b1Earrw4rhXNfXd8bipVTEeZs13QjHG1vHkGOqG9Wj9zo+enxJzc5fuSlWhpY3KeBhPgQqbB3/83N/sNOgW8v1UMH7SbE11Tjv6v55nzA+CyMy3sYZ22YIFG8QqJOv6iUeGKk1szgU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776713389; c=relaxed/simple; bh=KEGY4s5L8vddgO3MvEHaS3XpKhUKLKraGKWm1E7ZRm0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Qxcm1lrXwZD9cD+m1zHl9qIIZHPjiDfEkFELWkMo0dDEYC2Lh4U2gTs21JVcLjGL02DFd5x6UknuHi51RkB3UDNce1gutfxdigvZXO4/dfiKPnszEjR2phh/IMWECx+0wb1VYb7lJ3s3kQcFstor2Dc6nwwIzG87Zcl9e8CHjcw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=IxxpSCtm; 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="IxxpSCtm" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E5453C2BCB0; Mon, 20 Apr 2026 19:29:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776713389; bh=KEGY4s5L8vddgO3MvEHaS3XpKhUKLKraGKWm1E7ZRm0=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=IxxpSCtmgQ8r5uOHX3CS8mUlg7Q4a37vM06e/YT73FKCBbUmrQu+4Vj/89P5SYFKT R5MpM/cwzv9st9kD7vQxzKltEVryMB8H/9LpXQfafBSP2XiUskoWF/R4CFti4AA8cZ 1aNVhMQ2MhbL+Wp1OX5WO1wOAZ/oaxCX4ybz7G/QMEiIlYp4GJvFMSl2wh24uQyfm9 DqIrGGbdLU7k7AbJOcqxjDz01xd7cPHIWo2aPHmLyobKp/mYulTNaKeARvgFb0Q8Gl 6AN9PeobwjlTiEPvZA6wguXZgEUQHoPjKGBA1ba4cjyRlBufdLwuPVrZSkOnnosdyj XDH+iEPWyU04g== Message-ID: Date: Mon, 20 Apr 2026 21:29:43 +0200 Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 2/2] mm/gup: add lockless access semantics on entries validation To: Alexander Gordeev , Kevin Brodsky , Ryan Roberts , Andrew Morton Cc: linux-s390@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Gerald Schaefer , Heiko Carstens , Vasily Gorbik References: <55c295e17221dc882e09b4caddc7b3bf4f1309ba.1776684344.git.agordeev@linux.ibm.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 4/20/26 14:13, Alexander Gordeev wrote: > The PTE validation in gup_fast_pte_range() is inconsistent with the > prior value acquisition in the sense that it drops the lockless > access semantics. > > Although this is highly unlikely, prevent a future scenario in which > a semantically mismatching ptep_get() incorrectly yields the same > result as the preceding ptep_get_lockless(), while ptep_get_lockless() > would otherwise return a different value. > > Likewise the PMD validation is inconsistent with the prior value > acquisition in gup_fast_pmd_range(). > > Signed-off-by: Alexander Gordeev > --- > mm/gup.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/mm/gup.c b/mm/gup.c > index d149a4b0df71..236450feea9a 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -2865,8 +2865,8 @@ static int gup_fast_pte_range(pmd_t pmd, pmd_t *pmdp, unsigned long addr, > if (!folio) > goto pte_unmap; > > - if (unlikely(pmd_val(pmd) != pmd_val(pmdp_get(pmdp))) || > - unlikely(pte_val(pte) != pte_val(ptep_get(ptep)))) { > + if (unlikely(pmd_val(pmd) != pmd_val(pmdp_get_lockless(pmdp))) || > + unlikely(pte_val(pte) != pte_val(ptep_get_lockless(ptep)))) { > gup_put_folio(folio, 1, flags); > goto pte_unmap; > } > @@ -2942,7 +2942,7 @@ static int gup_fast_pmd_leaf(pmd_t orig, pmd_t *pmdp, unsigned long addr, > if (!folio) > return 0; > > - if (unlikely(pmd_val(orig) != pmd_val(pmdp_get(pmdp)))) { > + if (unlikely(pmd_val(orig) != pmd_val(pmdp_get_lockless(pmdp)))) { > gup_put_folio(folio, refs, flags); > return 0; > } Oh, that should be squashed into #1 :) -- Cheers, David