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

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Message-ID: <a8341dde-aa59-b425-ac23-b6005e0a67ec@arm.com>
Date:   Tue, 10 Mar 2020 19:16:42 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>
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>,
        Jeff Dike <jdike@...toit.com>,
        Richard Weinberger <richard@....at>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        Guan Xuetao <gxt@....edu.cn>, Chris Zankel <chris@...kel.net>,
        Max Filippov <jcmvbkbc@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-alpha@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        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,
        linux-xtensa@...ux-xtensa.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2] mm/special: Create generic fallbacks for pte_special()
 and pte_mkspecial()



On 03/10/2020 06:57 PM, Thomas Bogendoerfer wrote:
> 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.

I already had asked for clarification on this.

> 
> Why can't we use
> 
> #if defined(CONFIG_ARCH_HAS_PTE_SPECIAL)
> 
> here as the comment already suggests ?

Yes, that will be easier and will automatically adjust in case
ARCH_HAS_PTE_SPECIAL scope changes later. Will respin the patch.

> 
> Thomas.
>