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[217.140.101.70]) by mx.google.com with ESMTP id k52si492526edd.233.2019.02.22.02.21.45 for ; Fri, 22 Feb 2019 02:21:45 -0800 (PST) Received-SPF: pass (google.com: domain of steven.price@arm.com designates 217.140.101.70 as permitted sender) client-ip=217.140.101.70; Authentication-Results: mx.google.com; spf=pass (google.com: domain of steven.price@arm.com designates 217.140.101.70 as permitted sender) smtp.mailfrom=steven.price@arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id C24EB80D; Fri, 22 Feb 2019 02:21:44 -0800 (PST) Received: from [10.1.196.69] (e112269-lin.cambridge.arm.com [10.1.196.69]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A30923F703; Fri, 22 Feb 2019 02:21:41 -0800 (PST) Subject: Re: [PATCH v2 03/13] mm: Add generic p?d_large() macros To: "Kirill A. Shutemov" Cc: Mark Rutland , x86@kernel.org, Arnd Bergmann , Ard Biesheuvel , Peter Zijlstra , Catalin Marinas , Dave Hansen , Will Deacon , linux-kernel@vger.kernel.org, linux-mm@kvack.org, =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , Ingo Molnar , Borislav Petkov , Andy Lutomirski , "H. Peter Anvin" , James Morse , Thomas Gleixner , linux-arm-kernel@lists.infradead.org, "Liang, Kan" References: <20190221113502.54153-1-steven.price@arm.com> <20190221113502.54153-4-steven.price@arm.com> <20190221142812.oa53lfnnfmsuh6ys@kshutemo-mobl1> <20190221145706.zqwfdoyiirn3lc7y@kshutemo-mobl1> <20190221210618.voyfs5cnafpvgedh@kshutemo-mobl1> From: Steven Price Message-ID: <9441949b-6982-eea3-a05e-e277776ff821@arm.com> Date: Fri, 22 Feb 2019 10:21:40 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.0 MIME-Version: 1.0 In-Reply-To: <20190221210618.voyfs5cnafpvgedh@kshutemo-mobl1> Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: 7bit X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 21/02/2019 21:06, Kirill A. Shutemov wrote: > On Thu, Feb 21, 2019 at 05:16:46PM +0000, Steven Price wrote: >>>> Note that in terms of the new page walking code, these new defines are >>>> only used when walking a page table without a VMA (which isn't currently >>>> done), so architectures which don't use p?d_large currently will work >>>> fine with the generic versions. They only need to provide meaningful >>>> definitions when switching to use the walk-without-a-VMA functionality. >>> >>> How other architectures would know that they need to provide the helpers >>> to get walk-without-a-VMA functionality? This looks very fragile to me. >> >> Yes, you've got a good point there. This would apply to the p?d_large >> macros as well - any arch which (inadvertently) uses the generic version >> is likely to be fragile/broken. >> >> I think probably the best option here is to scrap the generic versions >> altogether and simply introduce a ARCH_HAS_PXD_LARGE config option which >> would enable the new functionality to those arches that opt-in. Do you >> think this would be less fragile? > > These helpers are useful beyond pagewalker. > > Can we actually do some grinding and make *all* archs to provide correct > helpers? Yes, it's tedious, but not that bad. > > I think we could provide generic helpers for folded levels in > and rest has to be provided by the arch. > Architectures that support only 2 level paging would need to provide > pgd_large(), with 3 -- pmd_large() and so on. Fair enough, I'll have a go and hopefully people will be able to correct it if I make any mistakes - I'm certainly not going to be able to test all architectures myself. Steve