netdev - Re: [PATCH v13 16/20] IB/mlx4, arm64: untag user pointers in mlx4_get_umem

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Message-ID: <20190502184442.GA31165@ziepe.ca>
Date:   Thu, 2 May 2019 15:44:42 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     Leon Romanovsky <leon@...nel.org>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Will Deacon <will.deacon@....com>,
        Robin Murphy <robin.murphy@....com>,
        Kees Cook <keescook@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Eric Dumazet <edumazet@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Yishai Hadas <yishaih@...lanox.com>,
        linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, netdev@...r.kernel.org,
        linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>,
        Evgeniy Stepanov <eugenis@...gle.com>,
        Ramana Radhakrishnan <Ramana.Radhakrishnan@....com>,
        Ruben Ayrapetyan <Ruben.Ayrapetyan@....com>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Dave Martin <Dave.Martin@....com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        Szabolcs Nagy <Szabolcs.Nagy@....com>
Subject: Re: [PATCH v13 16/20] IB/mlx4, arm64: untag user pointers in
 mlx4_get_umem_mr

On Tue, Apr 30, 2019 at 12:16:25PM +0100, Catalin Marinas wrote:
> > Interesting, the followup question is why mlx4 is only one driver in IB which
> > needs such code in umem_mr. I'll take a look on it.
> 
> I don't know. Just using the light heuristics of find_vma() shows some
> other places. For example, ib_umem_odp_get() gets the umem->address via
> ib_umem_start(). This was previously set in ib_umem_get() as called from
> mlx4_get_umem_mr(). Should the above patch have just untagged "start" on
> entry?

I have a feeling that there needs to be something for this in the odp
code..

Presumably mmu notifiers and what not also use untagged pointers? Most
likely then the umem should also be storing untagged pointers.

This probably becomes problematic because we do want the tag in cases
talking about the base VA of the MR..

Jason