linux-kernel - Re: [PATCH v19 02/15] arm64: Introduce prctl() options to control the tagged user addresses ABI

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Date:   Thu, 1 Aug 2019 09:45:05 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Kevin Brodsky <kevin.brodsky@....com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, amd-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-rdma@...r.kernel.org,
        linux-media@...r.kernel.org, kvm@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kees Cook <keescook@...omium.org>,
        Yishai Hadas <yishaih@...lanox.com>,
        Felix Kuehling <Felix.Kuehling@....com>,
        Alexander Deucher <Alexander.Deucher@....com>,
        Christian Koenig <Christian.Koenig@....com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Jens Wiklander <jens.wiklander@...aro.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Leon Romanovsky <leon@...nel.org>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Dave Martin <Dave.Martin@....com>,
        Khalid Aziz <khalid.aziz@...cle.com>, enh <enh@...gle.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Christoph Hellwig <hch@...radead.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>,
        Evgeniy Stepanov <eugenis@...gle.com>,
        Lee Smith <Lee.Smith@....com>,
        Ramana Radhakrishnan <Ramana.Radhakrishnan@....com>,
        Jacob Bramley <Jacob.Bramley@....com>,
        Ruben Ayrapetyan <Ruben.Ayrapetyan@....com>,
        Robin Murphy <robin.murphy@....com>,
        Szabolcs Nagy <Szabolcs.Nagy@....com>
Subject: Re: [PATCH v19 02/15] arm64: Introduce prctl() options to control the
 tagged user addresses ABI

On 8/1/19 5:38 AM, Kevin Brodsky wrote:
> This patch series only changes what is allowed or not at the syscall
> interface. It does not change the address space size. On arm64, TBI (Top
> Byte Ignore) has always been enabled for userspace, so it has never been
> possible to use the upper 8 bits of user pointers for addressing.

Oh, so does the address space that's available already chop that out?

> If other architectures were to support a similar functionality, then I
> agree that a common and more generic interface (if needed) would be
> helpful, but as it stands this is an arm64-specific prctl, and on arm64
> the address tag is defined by the architecture as bits [63:56].

It should then be an arch_prctl(), no?