From mboxrd@z Thu Jan  1 00:00:00 1970
From: Al Viro <viro@zeniv.linux.org.uk>
Subject: Re: [PATCH 09/14] m68k: drop custom __access_ok()
Date: Tue, 15 Feb 2022 07:13:42 +0000
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To: Christoph Hellwig <hch@lst.de>
Cc: Arnd Bergmann <arnd@kernel.org>, Linus Torvalds <torvalds@linux-foundation.org>, linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-api@vger.kernel.org, arnd@arndb.de, linux-kernel@vger.kernel.org, linux@armlinux.org.uk, will@kernel.org, guoren@kernel.org, bcain@codeaurora.org, geert@linux-m68k.org, monstr@monstr.eu, tsbogend@alpha.franken.de, nickhu@andestech.com, green.hu@gmail.com, dinguyen@kernel.org, shorne@gmail.com, deller@gmx.de, mpe@ellerman.id.au, peterz@infradead.org, mingo@redhat.com, mark.rutland@arm.com, hca@linux.ibm.com, dalias@libc.org, davem@davemloft.net, richard@nod.at, x86@kernel.org, jcmvbkbc@gmail.com, ebiederm@xmission.com, akpm@linux-foundation.org, ardb@kernel.org, linux-alpha@vger.kernel.org, linux-snps-arc@lists.infradead.org, linux-arm-kernel

On Tue, Feb 15, 2022 at 07:29:42AM +0100, Christoph Hellwig wrote:
> On Tue, Feb 15, 2022 at 12:37:41AM +0000, Al Viro wrote:
> > Perhaps simply wrap that sucker into #ifdef CONFIG_CPU_HAS_ADDRESS_SPACES
> > (and trim the comment down to "coldfire and 68000 will pick generic
> > variant")?
> 
> I wonder if we should invert CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE,
> select the separate address space config for s390, sparc64, non-coldfire
> m68k and mips with EVA and then just have one single access_ok for
> overlapping address space (as added by Arnd) and non-overlapping ones
> (always return true).

parisc is also such...  How about

	select ALTERNATE_SPACE_USERLAND

for that bunch?  While we are at it, how many unusual access_ok() instances are
left after this series?  arm64, itanic, um, anything else?

FWIW, sparc32 has a slightly unusual instance (see uaccess_32.h there); it's
obviously cheaper than generic and I wonder if the trick is legitimate (and
applicable elsewhere, perhaps)...