From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-s390-owner@vger.kernel.org>
Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56702 "EHLO
        lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1731437AbgIHQPM (ORCPT
        <rfc822;linux-s390@vger.kernel.org>); Tue, 8 Sep 2020 12:15:12 -0400
Received: from mail-qk1-x741.google.com (mail-qk1-x741.google.com [IPv6:2607:f8b0:4864:20::741])
        by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 52E59C061232
        for <linux-s390@vger.kernel.org>; Tue,  8 Sep 2020 06:26:13 -0700 (PDT)
Received: by mail-qk1-x741.google.com with SMTP id f142so15156366qke.13
        for <linux-s390@vger.kernel.org>; Tue, 08 Sep 2020 06:26:13 -0700 (PDT)
Date: Tue, 8 Sep 2020 10:26:10 -0300
From: Jason Gunthorpe <jgg@ziepe.ca>
Subject: Re: [RFC PATCH v2 2/3] mm: make pXd_addr_end() functions page-table
 entry aware
Message-ID: <20200908132610.GB87483@ziepe.ca>
References: <20200907180058.64880-1-gerald.schaefer@linux.ibm.com>
 <20200907180058.64880-3-gerald.schaefer@linux.ibm.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20200907180058.64880-3-gerald.schaefer@linux.ibm.com>
Sender: linux-s390-owner@vger.kernel.org
List-ID: <linux-s390.vger.kernel.org>
To: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: John Hubbard <jhubbard@nvidia.com>, LKML <linux-kernel@vger.kernel.org>, linux-mm <linux-mm@kvack.org>, linux-arch <linux-arch@vger.kernel.org>, Andrew Morton <akpm@linux-foundation.org>, Linus Torvalds <torvalds@linux-foundation.org>, Russell King <linux@armlinux.org.uk>, Mike Rapoport <rppt@kernel.org>, Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will@kernel.org>, Michael Ellerman <mpe@ellerman.id.au>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, Paul Mackerras <paulus@samba.org>, Jeff Dike <jdike@addtoit.com>, Richard Weinberger <richard@nod.at>, Dave Hansen <dave.hansen@linux.intel.com>, Andy Lutomirski <luto@kernel.org>, Peter Zijlstra <peterz@infradead.org>, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>, Arnd Bergmann <arnd@arndb.de>, Andrey Ryabinin <aryabinin@virtuozzo.com>, linux-x86 <x86@kernel.org>, linux-arm <linux-arm-kernel@lists.infradead.org>, linux-power <linuxppc-dev@lists.ozlabs.org>, linux-sparc <sparclinux@vger.kernel.org>, linux-um <linux-um@lists.infradead.org>, linux-s390 <linux-s390@vger.kernel.org>, Alexander Gordeev <agordeev@linux.ibm.com>, Vasily Gorbik <gor@linux.ibm.com>, Heiko Carstens <hca@linux.ibm.com>, Christian Borntraeger <borntraeger@de.ibm.com>, Claudio Imbrenda <imbrenda@linux.ibm.com>

On Mon, Sep 07, 2020 at 08:00:57PM +0200, Gerald Schaefer wrote:
> From: Alexander Gordeev <agordeev@linux.ibm.com>
> 
> Unlike all other page-table abstractions pXd_addr_end() do not take
> into account a particular table entry in which context the functions
> are called. On architectures with dynamic page-tables folding that
> might lead to lack of necessary information that is difficult to
> obtain other than from the table entry itself. That already led to
> a subtle memory corruption issue on s390.
> 
> By letting pXd_addr_end() functions know about the page-table entry
> we allow archs not only make extra checks, but also optimizations.
> 
> As result of this change the pXd_addr_end_folded() functions used
> in gup_fast traversal code become unnecessary and get replaced with
> universal pXd_addr_end() variants.
> 
> The arch-specific updates not only add dereferencing of page-table
> entry pointers, but also small changes to the code flow to make those
> dereferences possible, at least for x86 and powerpc. Also for arm64,
> but in way that should not have any impact.
> 
> So, even though the dereferenced page-table entries are not used on
> archs other than s390, and are optimized out by the compiler, there
> is a small change in kernel size and this is what bloat-o-meter reports:

This looks pretty clean and straightfoward, only
__munlock_pagevec_fill() had any real increased complexity.

Thanks,
Jason