From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <mark.rutland@arm.com>
Date: Tue, 15 Feb 2022 10:39:06 +0000
From: Mark Rutland <mark.rutland@arm.com>
Subject: Re: [PATCH 08/14] arm64: simplify access_ok()
Message-ID: <YguCysZGYYWUhAPk@FVFF77S0Q05N>
References: <20220214163452.1568807-1-arnd@kernel.org>
 <20220214163452.1568807-9-arnd@kernel.org>
 <CAMj1kXHixUFjV=4m3tzfGz7AiRWc-VczymbKuZq7dyZZNuLKxQ@mail.gmail.com>
 <CAK8P3a2VfvDkueaJNTA9SiB+PFsi_Q17AX+aL46ueooW2ahmQw@mail.gmail.com>
 <CAMj1kXGkG0KMD2rnKAJc3V7X9LP1grbcHTNYMnj_q4GiYfG2pQ@mail.gmail.com>
 <CAK8P3a0NTqK_m7q909d8FN6is8k4_u3zeckC9XOrjEi7kqSvmg@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAK8P3a0NTqK_m7q909d8FN6is8k4_u3zeckC9XOrjEi7kqSvmg@mail.gmail.com>
To: Arnd Bergmann <arnd@kernel.org>
Cc: Ard Biesheuvel <ardb@kernel.org>, Linus Torvalds <torvalds@linux-foundation.org>, Christoph Hellwig <hch@lst.de>, linux-arch <linux-arch@vger.kernel.org>, Linux Memory Management List <linux-mm@kvack.org>, Linux API <linux-api@vger.kernel.org>, Arnd Bergmann <arnd@arndb.de>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Russell King <linux@armlinux.org.uk>, Will Deacon <will@kernel.org>, Guo Ren <guoren@kernel.org>, Brian Cain <bcain@codeaurora.org>, Geert Uytterhoeven <geert@linux-m68k.org>, Michal Simek <monstr@monstr.eu>, Thomas Bogendoerfer <tsbogend@alpha.franken.de>, Nick Hu <nickhu@andestech.com>, Greentime Hu <green.hu@gmail.com>, Dinh Nguyen <dinguyen@kernel.org>, Stafford Horne <shorne@gmail.com>, Helge Deller <deller@gmx.de>, Michael Ellerman <mpe@ellerman.id.au>, Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>, Heiko Carstens <hca@linux.ibm.com>, Rich Felker <dalias@libc.org>, "David S. Miller" <davem@davemloft.net>, Richard Weinberger <richard@nod.at>, X86 ML <x86@kernel.org>, Max Filippov <jcmvbkbc@gmail.com>, "Eric W. Biederman" <ebiederm@xmission.com>, Andrew Morton <akpm@linux-foundation.org>, alpha <linux-alpha@vger.kernel.org>, "open list:SYNOPSYS ARC ARCHITECTURE" <linux-snps-arc@lists.infradead.org>, Linux ARM <linux-arm-kernel@lists.infradead.org>, linux-csky@vger.kernel.org, "open list:QUALCOMM HEXAGON..." <linux-hexagon@vger.kernel.org>, linux-ia64@vger.kernel.org, linux-m68k <linux-m68k@lists.linux-m68k.org>, "open list:MIPS" <linux-mips@vger.kernel.org>, Openrisc <openrisc@lists.librecores.org>, "open list:PARISC ARCHITECTURE" <linux-parisc@vger.kernel.org>, "open list:LINUX FOR POWERPC (32-BIT AND 64-BIT)" <linuxppc-dev@lists.ozlabs.org>, linux-riscv <linux-riscv@lists.infradead.org>, "open list:S390" <linux-s390@vger.kernel.org>, Linux-sh list <linux-sh@vger.kernel.org>, "open list:SPARC + UltraSPARC (sparc/sparc64)" <sparclinux@vger.kernel.org>, linux-um <linux-um@lists.infradead.org>, "open list:TENSILICA XTENSA PORT (xtensa)" <linux-xtensa@linux-xtensa.org>, Robin Murphy <robin.murphy@arm.com>
List-ID: <linux-um.lists.infradead.org>

On Tue, Feb 15, 2022 at 10:39:46AM +0100, Arnd Bergmann wrote:
> On Tue, Feb 15, 2022 at 10:21 AM Ard Biesheuvel <ardb@kernel.org> wrote:
> > On Tue, 15 Feb 2022 at 10:13, Arnd Bergmann <arnd@kernel.org> wrote:
> >
> > arm64 also has this leading up to the range check, and I think we'd no
> > longer need it:
> >
> >     if (IS_ENABLED(CONFIG_ARM64_TAGGED_ADDR_ABI) &&
> >         (current->flags & PF_KTHREAD || test_thread_flag(TIF_TAGGED_ADDR)))
> >             addr = untagged_addr(addr);
> 
> I suspect the expensive part here is checking the two flags, as untagged_addr()
> seems to always just add a sbfx instruction. Would this work?
> 
> #ifdef CONFIG_ARM64_TAGGED_ADDR_ABI
> #define access_ok(ptr, size) __access_ok(untagged_addr(ptr), (size))
> #else // the else path is the default, this can be left out.
> #define access_ok(ptr, size) __access_ok((ptr), (size))
> #endif

This would be an ABI change, e.g. for tasks without TIF_TAGGED_ADDR.

I don't think we should change this as part of this series.

Thanks,
Mark.