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Date:   Tue, 27 Jul 2021 20:38:31 +0200
From:   Heiko Carstens <hca@linux.ibm.com>
To:     Arnd Bergmann <arnd@kernel.org>
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>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        "David S. Miller" <davem@davemloft.net>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        the arch/x86 maintainers <x86@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
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        Linux-MM <linux-mm@kvack.org>, Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH v5 4/6] mm: simplify compat numa syscalls
Message-ID: <YQBSpxZR4P/Phpf1@osiris>
References: <20210727144859.4150043-1-arnd@kernel.org>
 <20210727144859.4150043-5-arnd@kernel.org>
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 <CAK8P3a3itgCyc4jDBodTOcwG+XXsDYspZqQVBmy88cGXevY5Yw@mail.gmail.com>
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On Tue, Jul 27, 2021 at 07:40:05PM +0200, Arnd Bergmann wrote:
> On Tue, Jul 27, 2021 at 7:27 PM Heiko Carstens <hca@linux.ibm.com> wrote:
> > > +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.

What I was trying to say: this patch on its own is ok. However with
the next patch you remove the compat system calls and map the regular
system calls instead.

That is:

-COMPAT_SYSCALL_DEFINE6(mbind, compat_ulong_t, start, compat_ulong_t, len,
-		       compat_ulong_t, mode, compat_ulong_t __user *, nmask,
-		       compat_ulong_t, maxnode, compat_ulong_t, flags)
-{
-	return kernel_mbind(start, len, mode, (unsigned long __user *)nmask,
-			    maxnode, flags);
-}

and this:

-268  common	mbind			sys_mbind			compat_sys_mbind
-269  common	get_mempolicy		sys_get_mempolicy		compat_sys_get_mempolicy
-270  common	set_mempolicy		sys_set_mempolicy		compat_sys_set_mempolicy
+268  common	mbind			sys_mbind			sys_mbind
+269  common	get_mempolicy		sys_get_mempolicy		sys_get_mempolicy
+270  common	set_mempolicy		sys_set_mempolicy		sys_set_mempolicy

would remove compat_ptr() conversion from nmask above if I'm not mistaken.