linux-kernel - Re: [PATCH V3 09/30] arm/mm: Enable ARCH_HAS_VM_GET_PAGE

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Date:   Wed, 2 Mar 2022 11:19:22 +0000
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        "linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>,
        "linux-sh@...r.kernel.org" <linux-sh@...r.kernel.org>,
        "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "sparclinux@...r.kernel.org" <sparclinux@...r.kernel.org>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        "linux-hexagon@...r.kernel.org" <linux-hexagon@...r.kernel.org>,
        "linux-csky@...r.kernel.org" <linux-csky@...r.kernel.org>,
        Christoph Hellwig <hch@...radead.org>,
        "linux-snps-arc@...ts.infradead.org" 
        <linux-snps-arc@...ts.infradead.org>,
        "linux-xtensa@...ux-xtensa.org" <linux-xtensa@...ux-xtensa.org>,
        Arnd Bergmann <arnd@...db.de>,
        "linux-um@...ts.infradead.org" <linux-um@...ts.infradead.org>,
        "linux-m68k@...ts.linux-m68k.org" <linux-m68k@...ts.linux-m68k.org>,
        "openrisc@...ts.librecores.org" <openrisc@...ts.librecores.org>,
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        <linux-arm-kernel@...ts.infradead.org>,
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        "linux-alpha@...r.kernel.org" <linux-alpha@...r.kernel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH V3 09/30] arm/mm: Enable ARCH_HAS_VM_GET_PAGE_PROT

On Wed, Mar 02, 2022 at 04:36:52PM +0530, Anshuman Khandual wrote:
> On 3/2/22 3:35 PM, Geert Uytterhoeven wrote:
> > I doubt the switch() variant would give better code on any platform.
> > 
> > What about using tables everywhere, using designated initializers
> > to improve readability?
> 
> Designated initializers ? Could you please be more specific. A table look
> up on arm platform would be something like this and arm_protection_map[]
> needs to be updated with user_pgprot like before.

There is *absolutely* nothing wrong with that. Updating it once during
boot is way more efficient than having to compute the value each time
vm_get_page_prot() gets called.

Thanks.

-- 
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