linux-kernel - Re: [PATCH v16 04/16] mm: untag user pointers in do_pages

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Date:   Wed, 12 Jun 2019 13:08:35 +0200
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Khalid Aziz <khalid.aziz@...cle.com>
Cc:     Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <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,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        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>, 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>,
        Kevin Brodsky <kevin.brodsky@....com>,
        Szabolcs Nagy <Szabolcs.Nagy@....com>
Subject: Re: [PATCH v16 04/16] mm: untag user pointers in do_pages_move

On Tue, Jun 11, 2019 at 10:18 PM Khalid Aziz <khalid.aziz@...cle.com> wrote:
>
> On 6/3/19 10:55 AM, Andrey Konovalov wrote:
> > This patch is a part of a series that extends arm64 kernel ABI to allow to
> > pass tagged user pointers (with the top byte set to something else other
> > than 0x00) as syscall arguments.
> >
> > do_pages_move() is used in the implementation of the move_pages syscall.
> >
> > Untag user pointers in this function.
> >
> > Reviewed-by: Catalin Marinas <catalin.marinas@....com>
> > Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
> > ---
> >  mm/migrate.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/mm/migrate.c b/mm/migrate.c
> > index f2ecc2855a12..3930bb6fa656 100644
> > --- a/mm/migrate.c
> > +++ b/mm/migrate.c
> > @@ -1617,6 +1617,7 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
> >               if (get_user(node, nodes + i))
> >                       goto out_flush;
> >               addr = (unsigned long)p;
> > +             addr = untagged_addr(addr);
>
> Why not just "addr = (unsigned long)untagged_addr(p);"

Will do in the next version. I think I'll also merge this commit into
the "untag user pointers passed to memory syscalls" one.

>
> --
> Khalid
>