Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Wed, 10 May 2023 07:07:15 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Hugh Dickins <hughd@google.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Mike Rapoport <rppt@kernel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        David Hildenbrand <david@redhat.com>,
        Suren Baghdasaryan <surenb@google.com>,
        Qi Zheng <zhengqi.arch@bytedance.com>,
        Russell King <linux@armlinux.org.uk>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Greg Ungerer <gerg@linux-m68k.org>,
        Michal Simek <monstr@monstr.eu>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        Helge Deller <deller@gmx.de>,
        John David Anglin <dave.anglin@bell.net>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Alexandre Ghiti <alexghiti@rivosinc.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Heiko Carstens <hca@linux.ibm.com>,
        Christian Borntraeger <borntraeger@linux.ibm.com>,
        Claudio Imbrenda <imbrenda@linux.ibm.com>,
        John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>,
        "David S. Miller" <davem@davemloft.net>,
        Chris Zankel <chris@zankel.net>,
        Max Filippov <jcmvbkbc@gmail.com>, x86@kernel.org,
        linux-arm-kernel@lists.infradead.org, linux-ia64@vger.kernel.org,
        linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org,
        linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org,
        linux-sh@vger.kernel.org, sparclinux@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH 00/23] arch: allow pte_offset_map[_lock]() to fail
Message-ID: <ZFs0k2rrLPH9A/UU@casper.infradead.org>
References: <77a5d8c-406b-7068-4f17-23b7ac53bc83@google.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <77a5d8c-406b-7068-4f17-23b7ac53bc83@google.com>
Precedence: bulk

On Tue, May 09, 2023 at 09:39:13PM -0700, Hugh Dickins wrote:
> Two: pte_offset_map() will need to do an rcu_read_lock(), with the
> corresponding rcu_read_unlock() in pte_unmap().  But most architectures
> never supported CONFIG_HIGHPTE, so some don't always call pte_unmap()
> after pte_offset_map(), or have used userspace pte_offset_map() where
> pte_offset_kernel() is more correct.  No problem in the current tree,
> but a problem once an rcu_read_unlock() will be needed to keep balance.

Hi Hugh,

I shall have to spend some time looking at these patches, but at LSFMM
just a few hours ago, I proposed and nobody objected to removing
CONFIG_HIGHPTE.  I don't intend to take action on that consensus
immediately, so I can certainly wait until your patches are applied, but
if this information simplifies what you're doing, feel free to act on it.