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From:   Arnd Bergmann <arnd@kernel.org>
Date:   Tue, 27 Jul 2021 19:40:05 +0200
Message-ID: <CAK8P3a3itgCyc4jDBodTOcwG+XXsDYspZqQVBmy88cGXevY5Yw@mail.gmail.com>
Subject: Re: [PATCH v5 4/6] mm: simplify compat numa syscalls
To:     Heiko Carstens <hca@linux.ibm.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        "James E.J. Bottomley" <James.Bottomley@hansenpartnership.com>,
        Helge Deller <deller@gmx.de>,
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        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
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        "the arch/x86 maintainers" <x86@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
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On Tue, Jul 27, 2021 at 7:27 PM Heiko Carstens <hca@linux.ibm.com> wrote:
>
> On Tue, Jul 27, 2021 at 04:48:57PM +0200, Arnd Bergmann wrote:
> > ---
> >  include/linux/compat.h |  17 ++--
> >  mm/mempolicy.c         | 175 +++++++++++++----------------------------
> >  2 files changed, 63 insertions(+), 129 deletions(-)
> ...
> > +static int get_bitmap(unsigned long *mask, const unsigned long __user *nmask,
> > +                   unsigned long maxnode)
> > +{
> > +     unsigned long nlongs = BITS_TO_LONGS(maxnode);
> > +     int ret;
> > +
> > +     if (in_compat_syscall())
> > +             ret = compat_get_bitmap(mask,
> > +                                     (const compat_ulong_t __user *)nmask,
> > +                                     maxnode);
>
> compat_ptr() conversion for e.g. nmask is missing with the next patch
> which removes the compat system calls.
> Is that intended or am I missing something?

I don't think it's needed here, since the pointer comes from the system
call argument, which has the compat_ptr() conversion applied in
arch/s390/include/asm/syscall_wrapper.h, not from a compat_uptr_t
that gets passed indirectly. The compat_get_bitmap() conversion
is only needed for byte order adjustment, not for converting pointers.

It's also possible that I'm the one who's missing something.

        Arnd