linux-kernel - Re: [RFC v2 01/39] Kconfig: introduce HAS_IOPORT option and select it as necessary

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Message-ID: <7b8d7c1a-58c3-4ba9-a4f0-d0e051f3ffdc@huawei.com>
Date:   Fri, 6 May 2022 12:07:26 +0100
From:   John Garry <john.garry@...wei.com>
To:     Niklas Schnelle <schnelle@...ux.ibm.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Arnd Bergmann <arnd@...nel.org>
CC:     Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        linux-pci <linux-pci@...r.kernel.org>,
        Richard Henderson <rth@...ddle.net>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        Matt Turner <mattst88@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Michal Simek <monstr@...str.eu>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        "James E.J. Bottomley" <James.Bottomley@...senpartnership.com>,
        Helge Deller <deller@....de>,
        Michael Ellerman <mpe@...erman.id.au>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        "Rich Felker" <dalias@...c.org>,
        "David S. Miller" <davem@...emloft.net>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "Borislav Petkov" <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        "open list:ALPHA PORT" <linux-alpha@...r.kernel.org>,
        "moderated list:ARM PORT" <linux-arm-kernel@...ts.infradead.org>,
        "open list:IA64 (Itanium) PLATFORM" <linux-ia64@...r.kernel.org>,
        "open list:M68K ARCHITECTURE" <linux-m68k@...ts.linux-m68k.org>,
        "open list:MIPS" <linux-mips@...r.kernel.org>,
        "open list:PARISC ARCHITECTURE" <linux-parisc@...r.kernel.org>,
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        <sparclinux@...r.kernel.org>
Subject: Re: [RFC v2 01/39] Kconfig: introduce HAS_IOPORT option and select it
 as necessary

On 06/05/2022 10:38, Niklas Schnelle wrote:
> Another argument I see is that as shown by POWER9 we might start to see
> more platforms that just can't do I/O port access. E.g. I would also be
> surprised if Apple's M1 has I/O port access. Sooner or later I expect
> distributions on some platforms to only support such systems. For
> example on ppc a server distribution might only support IBM POWER
> without I/O port support before too long. Then having HAS_IOPORT allows
> to get rid of drivers that won't work anyway.
> 
> There are also reports of probing a driver with I/O ports causing a
> system crash on systems without I/O port support. For example in this
> answer by John Garry (added so he may supply more information):
> 
> https://lore.kernel.org/lkml/db043b76-880d-5fad-69cf-96abcd9cd34f@huawei.com/
> 
> .

That issue is that drivers like hwmon f71805f use inb/outb accessors 
with hardcoded IO port addresses to probe the driver. On archs like 
arm64 or powerpc - which do not natively support inb et al - this may 
crash the system when no PCI IO space is mapped [0]. Indeed, when PCI IO 
space is mapped, it is preferable these those drivers still would not 
access these ports.

So this series from Niklas could be used as a basis to solve that 
problem, in that we could also introduce something like HARDCODED_IOPORT 
[1] to stop those drivers being built at all for arm64.

[0] 
https://lore.kernel.org/linux-input/20210112055129.7840-1-song.bao.hua@hisilicon.com/T/#mf86445470160c44ac110e9d200b09245169dc5b6
[1] 
https://lore.kernel.org/lkml/CAK8P3a3HHeP+Gw_k2P7Qtig0OmErf0HN30G22+qHic_uZTh11Q@mail.gmail.com/

Thanks,
John