linux-kernel - Re: [PATCH V2] mm/special: Create generic fallbacks for pte_special() and pte

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Message-ID: <20200310132747.GA12601@alpha.franken.de>
Date:   Tue, 10 Mar 2020 14:27:47 +0100
From:   Thomas Bogendoerfer <tsbogend@...ha.franken.de>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-mm@...ck.org, Richard Henderson <rth@...ddle.net>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        Matt Turner <mattst88@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Guo Ren <guoren@...nel.org>, Brian Cain <bcain@...eaurora.org>,
        Tony Luck <tony.luck@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Sam Creasey <sammy@...my.net>, Michal Simek <monstr@...str.eu>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paulburton@...nel.org>,
        Nick Hu <nickhu@...estech.com>,
        Greentime Hu <green.hu@...il.com>,
        Vincent Chen <deanbo422@...il.com>,
        Ley Foon Tan <ley.foon.tan@...el.com>,
        Jonas Bonn <jonas@...thpole.se>,
        Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>,
        Stafford Horne <shorne@...il.com>,
        "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>,
        Helge Deller <deller@....de>,
        "David S. Miller" <davem@...emloft.net>,
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        Guan Xuetao <gxt@....edu.cn>, Chris Zankel <chris@...kel.net>,
        Max Filippov <jcmvbkbc@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
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        linux-csky@...r.kernel.org, linux-hexagon@...r.kernel.org,
        linux-ia64@...r.kernel.org, linux-m68k@...ts.linux-m68k.org,
        linux-mips@...r.kernel.org, nios2-dev@...ts.rocketboards.org,
        openrisc@...ts.librecores.org, linux-parisc@...r.kernel.org,
        sparclinux@...r.kernel.org, linux-um@...ts.infradead.org,
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        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2] mm/special: Create generic fallbacks for
 pte_special() and pte_mkspecial()

On Tue, Mar 10, 2020 at 06:39:11AM +0530, Anshuman Khandual wrote:
> diff --git a/arch/mips/include/asm/pgtable.h b/arch/mips/include/asm/pgtable.h
> index aef5378f909c..8e4e4be1ca00 100644
> --- a/arch/mips/include/asm/pgtable.h
> +++ b/arch/mips/include/asm/pgtable.h
> @@ -269,6 +269,36 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
>   */
>  extern pgd_t swapper_pg_dir[];
>  
> +/*
> + * Platform specific pte_special() and pte_mkspecial() definitions
> + * are required only when ARCH_HAS_PTE_SPECIAL is enabled.
> + */
> +#if !defined(CONFIG_32BIT) && !defined(CONFIG_CPU_HAS_RIXI)

this looks wrong.

current Kconfig statement is

select ARCH_HAS_PTE_SPECIAL if !(32BIT && CPU_HAS_RIXI)

so we can't use PTE_SPECIAL on 32bit _and_ CPUs with RIXI support.

Why can't we use

#if defined(CONFIG_ARCH_HAS_PTE_SPECIAL)

here as the comment already suggests ?

Thomas.

-- 
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea.                                                [ RFC1925, 2.3 ]