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From:   Andrey Konovalov <andreyknvl@google.com>
Date:   Mon, 18 Mar 2019 14:16:54 +0100
Message-ID: <CAAeHK+yxcG=KBjG0A5BicBA7Zwu6LR6t=g5b-9EAPXA8_Dfm2g@mail.gmail.com>
Subject: Re: [PATCH v11 08/14] net, arm64: untag user pointers in tcp_zerocopy_receive
To:     Eric Dumazet <eric.dumazet@gmail.com>
Cc:     Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        Mark Rutland <mark.rutland@arm.com>,
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        Andrew Morton <akpm@linux-foundation.org>,
        Ingo Molnar <mingo@kernel.org>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Shuah Khan <shuah@kernel.org>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        Eric Dumazet <edumazet@google.com>,
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        Alexei Starovoitov <ast@kernel.org>,
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On Mon, Mar 18, 2019 at 2:14 PM Andrey Konovalov <andreyknvl@google.com> wrote:
>
> On Fri, Mar 15, 2019 at 9:03 PM Eric Dumazet <eric.dumazet@gmail.com> wrote:
> >
> >
> >
> > On 03/15/2019 12:51 PM, 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.
> > >
> > > tcp_zerocopy_receive() uses provided user pointers for vma lookups, which
> > > can only by done with untagged pointers.
> > >
> > > Untag user pointers in this function.
> > >
> > > Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
> > > ---
> > >  net/ipv4/tcp.c | 2 ++
> > >  1 file changed, 2 insertions(+)
> > >
> > > diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> > > index 6baa6dc1b13b..89db3b4fc753 100644
> > > --- a/net/ipv4/tcp.c
> > > +++ b/net/ipv4/tcp.c
> > > @@ -1758,6 +1758,8 @@ static int tcp_zerocopy_receive(struct sock *sk,
> > >       int inq;
> > >       int ret;
> > >
> > > +     address = untagged_addr(address);
> > > +
> > >       if (address & (PAGE_SIZE - 1) || address != zc->address)
> >
> > The second test will fail, if the top bits are changed in address but not in zc->address
>
> Will fix in v12, thanks Eric!

Looking at the code, what's the point of this address != zc->address
check? Should I just remove it?

>
> >
> > >               return -EINVAL;
> > >
> > >
> >