linux-kernel - Re: [PATCH v16 12/16] IB, arm64: untag user pointers in ib_uverbs_(re)reg

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Message-ID: <20190604130207.GD15385@ziepe.ca>
Date:   Tue, 4 Jun 2019 10:02:07 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Andrey Konovalov <andreyknvl@...gle.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>,
        Khalid Aziz <khalid.aziz@...cle.com>, enh <enh@...gle.com>,
        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 12/16] IB, arm64: untag user pointers in
 ib_uverbs_(re)reg_mr()

On Tue, Jun 04, 2019 at 02:45:32PM +0200, Andrey Konovalov wrote:
> On Tue, Jun 4, 2019 at 2:27 PM Jason Gunthorpe <jgg@...pe.ca> wrote:
> >
> > On Tue, Jun 04, 2019 at 02:18:19PM +0200, Andrey Konovalov wrote:
> > > On Mon, Jun 3, 2019 at 7:46 PM Jason Gunthorpe <jgg@...pe.ca> wrote:
> > > >
> > > > On Mon, Jun 03, 2019 at 06:55:14PM +0200, 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.
> > > > >
> > > > > ib_uverbs_(re)reg_mr() use provided user pointers for vma lookups (through
> > > > > e.g. mlx4_get_umem_mr()), which can only by done with untagged pointers.
> > > > >
> > > > > Untag user pointers in these functions.
> > > > >
> > > > > Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
> > > > >  drivers/infiniband/core/uverbs_cmd.c | 4 ++++
> > > > >  1 file changed, 4 insertions(+)
> > > > >
> > > > > diff --git a/drivers/infiniband/core/uverbs_cmd.c b/drivers/infiniband/core/uverbs_cmd.c
> > > > > index 5a3a1780ceea..f88ee733e617 100644
> > > > > +++ b/drivers/infiniband/core/uverbs_cmd.c
> > > > > @@ -709,6 +709,8 @@ static int ib_uverbs_reg_mr(struct uverbs_attr_bundle *attrs)
> > > > >       if (ret)
> > > > >               return ret;
> > > > >
> > > > > +     cmd.start = untagged_addr(cmd.start);
> > > > > +
> > > > >       if ((cmd.start & ~PAGE_MASK) != (cmd.hca_va & ~PAGE_MASK))
> > > > >               return -EINVAL;
> > > >
> > > > I feel like we shouldn't thave to do this here, surely the cmd.start
> > > > should flow unmodified to get_user_pages, and gup should untag it?
> > > >
> > > > ie, this sort of direction for the IB code (this would be a giant
> > > > patch, so I didn't have time to write it all, but I think it is much
> > > > saner):
> > >
> > > Hi Jason,
> > >
> > > ib_uverbs_reg_mr() passes cmd.start to mlx4_get_umem_mr(), which calls
> > > find_vma(), which only accepts untagged addresses. Could you explain
> > > how your patch helps?
> >
> > That mlx4 is just a 'weird duck', it is not the normal flow, and I
> > don't think the core code should be making special consideration for
> > it.
> 
> How do you think we should do untagging (or something else) to deal
> with this 'weird duck' case?

mlx4 should handle it around the call to find_vma like other patches
do, ideally as part of the cast from a void __user * to the unsigned
long that find_vma needs

Jason