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[178.121.232.23]) by smtp.gmail.com with ESMTPSA id z85sm6143768lff.80.2019.02.21.13.06.20 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 21 Feb 2019 13:06:20 -0800 (PST) Received: by kshutemo-mobl1.localdomain (Postfix, from userid 1000) id E14B7301708; Fri, 22 Feb 2019 00:06:18 +0300 (+03) Date: Fri, 22 Feb 2019 00:06:18 +0300 From: "Kirill A. Shutemov" To: Steven Price Cc: Mark Rutland , Dave Hansen , Arnd Bergmann , Ard Biesheuvel , Peter Zijlstra , Catalin Marinas , x86@kernel.org, Will Deacon , linux-kernel@vger.kernel.org, linux-mm@kvack.org, =?utf-8?B?SsOpcsO0bWU=?= Glisse , Ingo Molnar , Borislav Petkov , Andy Lutomirski , "H. Peter Anvin" , James Morse , Thomas Gleixner , linux-arm-kernel@lists.infradead.org, "Liang, Kan" Subject: Re: [PATCH v2 03/13] mm: Add generic p?d_large() macros Message-ID: <20190221210618.voyfs5cnafpvgedh@kshutemo-mobl1> References: <20190221113502.54153-1-steven.price@arm.com> <20190221113502.54153-4-steven.price@arm.com> <20190221142812.oa53lfnnfmsuh6ys@kshutemo-mobl1> <20190221145706.zqwfdoyiirn3lc7y@kshutemo-mobl1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20180716 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 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. -- Kirill A. Shutemov