From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mta0.migadu.com (out-228.mta0.migadu.com [91.218.175.228])
	(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 07E67370AE7
	for <linux-kernel@vger.kernel.org>; Thu, 13 Aug 2026 15:49:47 +0000 (UTC)
Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.228
ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116;
	t=1786636196; cv=none; b=an3A29VZFAeAmDGCf1Wx9WmbpXQ1gjEAkvEGvx07lAWTRbYZFkI+xhHw4oro/qfS9RQQyutU3E67J1RpQTJ4ZavhShz0tzTEQxxdWnOLfYfIYMHoWnqQERQ7RHM6YB/h5iAj5PFrg4cdXiukLTv0K9VMh9BphvOm/r8WVCwGqdw=
ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org;
	s=arc-20240116; t=1786636196; c=relaxed/simple;
	bh=44TR69x5ZAwBqBOOwd22fnYBam5ymuntq7grA3Sn4D0=;
	h=Mime-Version:Content-Type:Date:Message-Id:Cc:Subject:From:To:
	 References:In-Reply-To; b=BZB0fca12VlE6qF5kQWrHbN+OB0xARO2VntVI8WkXd7PKv/n0VKHVf558Q858YNm+78s8TgW8IqJtuCF4qjec9snr6cN+Ez70CylC6hNpxnVDJLLXHk1pk/XWnGsiKoIfqoe6CYmABRUcJmfe3pWIwNRW7RXSetE+P7FvunynLE=
ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=xKKbj0tK; arc=none smtp.client-ip=91.218.175.228
Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev
Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev
Authentication-Results: smtp.subspace.kernel.org;
	dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="xKKbj0tK"
X-Envelope-To: linux-kernel@vger.kernel.org
DKIM-Signature: a=rsa-sha256; bh=44TR69x5ZAwBqBOOwd22fnYBam5ymuntq7grA3Sn4D0=;
 c=simple/simple; d=linux.dev;
 h=from:to:subject:date:message-id:mime-version:content-type; s=key1;
 t=1786636182; v=1; x=1787240982;
 b=xKKbj0tKLi0NSB6TAgaoQicyHfgBNzS3hxfGkPf7DNOsPu/l/MUGY32z8wHoKYkYkhr/iYkk
 tfKSReXZNkWsSD3Q06H5ImqVk449AEmV2Cmo/B24X5jFaDbgxdzIogkaPL/Xgsh4KC5ND7GILEj
 t0YzHznab2TmQnH6rrtqEhEg=
X-Envelope-To: linux-kernel@vger.kernel.org
Received: from localhost (77.97.51.77)
	by smtp.migadu.com with ESMTPS id 1965510105143205;
	Thu, 13 Aug 2026 15:49:42 +0000
X-Migadu-Flow: FLOW_OUT
Precedence: bulk
X-Mailing-List: linux-kernel@vger.kernel.org
List-Id: <linux-kernel.vger.kernel.org>
List-Subscribe: <mailto:linux-kernel+subscribe@vger.kernel.org>
List-Unsubscribe: <mailto:linux-kernel+unsubscribe@vger.kernel.org>
Mime-Version: 1.0
Content-Transfer-Encoding: quoted-printable
Content-Type: text/plain; charset=UTF-8
Date: Thu, 13 Aug 2026 16:49:40 +0100
Message-Id: <DKNXO2ODV6AN.C0CFRAHJJUA4@linux.dev>
Cc: "Borislav Petkov" <bp@alien8.de>, "Dave Hansen"
 <dave.hansen@linux.intel.com>, "Peter Zijlstra" <peterz@infradead.org>,
 "Andrew Morton" <akpm@linux-foundation.org>, "David Hildenbrand"
 <david@kernel.org>, "Vlastimil Babka" <vbabka@kernel.org>, "Mike Rapoport"
 <rppt@kernel.org>, "Wei Xu" <weixugc@google.com>, "Johannes Weiner"
 <hannes@cmpxchg.org>, "Zi Yan" <ziy@nvidia.com>, "Lorenzo Stoakes"
 <ljs@kernel.org>, <linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>,
 <x86@kernel.org>, "Sumit Garg" <sumit.garg@oss.qualcomm.com>, "Will Deacon"
 <will@kernel.org>, <rientjes@google.com>, "Kalyazin, Nikita"
 <kalyazin@amazon.co.uk>, <patrick.roy@linux.dev>, "Itazuri, Takahiro"
 <itazur@amazon.co.uk>, "Andy Lutomirski" <luto@kernel.org>, "David Kaplan"
 <david.kaplan@amd.com>, "Thomas Gleixner" <tglx@kernel.org>, "Patrick
 Bellasi" <derkling@google.com>, "Reiji Watanabe" <reijiw@google.com>, "Sean
 Christopherson" <seanjc@google.com>
Subject: Re: [PATCH v3 05/26] x86: move PAE PMD preallocation defines to
 header
From: "Brendan Jackman" <brendan.jackman@linux.dev>
To: "Yosry Ahmed" <yosry@kernel.org>, "Brendan Jackman"
 <jackmanb@google.com>
X-Mailer: aerc 0.21.0
References: <20260726-page_alloc-unmapped-v3-0-6f5729aa9832@google.com>
 <20260726-page_alloc-unmapped-v3-5-6f5729aa9832@google.com>
 <am02PmF4-lPErIVd@google.com>
In-Reply-To: <am02PmF4-lPErIVd@google.com>

On Sat Aug 1, 2026 at 12:59 AM BST, Yosry Ahmed wrote:
> On Sun, Jul 26, 2026 at 10:22:38PM +0000, Brendan Jackman wrote:
>> In a subsequent patch these defines will need to be referenced from a ne=
w
>> file, move them as a separate patch for easy review.
>>=20
>> The comments have style violations (personal pronouns etc), do not fix
>> them as this is just code movement.
>>=20
>> No functional change intended.
>>=20
>> Signed-off-by: Brendan Jackman <jackmanb@google.com>
>
> AFAICT, this is only needed to expose PREALLOCATED_PMDS for
> mm_local_map_to_user() in patch #7. The only usage is a BUILD_BUG_ON().
>
> I wonder if it would be more preferrable to keep the definitions in
> pgtable.c and add a runtime check instead in mm_local_map_to_user(),
> something like:
>
> diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mm=
u_context.h
> index 09b8d8e6a56ea..15055cb80092c 100644
> --- a/arch/x86/include/asm/mmu_context.h
> +++ b/arch/x86/include/asm/mmu_context.h
> @@ -268,7 +268,6 @@ static inline pmd_t *pgd_to_pmd_walk(pgd_t *pgd, unsi=
gned long va)
>
>  static inline int mm_local_map_to_user(struct mm_struct *mm)
>  {
> -       BUILD_BUG_ON(!PREALLOCATED_PMDS);
>         pgd_t *k_pgd =3D pgd_offset(mm, MM_LOCAL_BASE_ADDR);
>         pgd_t *u_pgd =3D kernel_to_user_pgdp(k_pgd);
>         pmd_t *k_pmd, *u_pmd;
> @@ -277,6 +276,9 @@ static inline int mm_local_map_to_user(struct mm_stru=
ct *mm)
>         k_pmd =3D pgd_to_pmd_walk(k_pgd, MM_LOCAL_BASE_ADDR);
>         u_pmd =3D pgd_to_pmd_walk(u_pgd, MM_LOCAL_BASE_ADDR);
>
> +       if (WARN_ON_ONCE(!k_pmd || !u_pmd))
> +               return -EINVAL;
> +
>         BUILD_BUG_ON(MM_LOCAL_END_ADDR - MM_LOCAL_BASE_ADDR > PMD_SIZE);
>
>         /* Preallocate the PTE table so it can be shared. */

Yeah, I'd say that's fine. Will get back to you if I find another reason
why I thought the move was necessary...