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[217.140.101.70]) by mx.google.com with ESMTP id v4si685084eji.337.2019.04.03.06.58.34 for ; Wed, 03 Apr 2019 06:58:34 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of robin.murphy@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: best guess record for domain of robin.murphy@arm.com designates 217.140.101.70 as permitted sender) smtp.mailfrom=robin.murphy@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 76FF6A78; Wed, 3 Apr 2019 06:58:33 -0700 (PDT) Received: from [10.1.196.75] (e110467-lin.cambridge.arm.com [10.1.196.75]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 196953F557; Wed, 3 Apr 2019 06:58:29 -0700 (PDT) Subject: Re: [PATCH 6/6] arm64/mm: Enable ZONE_DEVICE To: Anshuman Khandual , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, akpm@linux-foundation.org, will.deacon@arm.com, catalin.marinas@arm.com Cc: mhocko@suse.com, mgorman@techsingularity.net, james.morse@arm.com, mark.rutland@arm.com, cpandya@codeaurora.org, arunks@codeaurora.org, dan.j.williams@intel.com, osalvador@suse.de, logang@deltatee.com, david@redhat.com, cai@lca.pw, dan.j.williams@intel.com, jglisse@redhat.com References: <1554265806-11501-1-git-send-email-anshuman.khandual@arm.com> <1554265806-11501-7-git-send-email-anshuman.khandual@arm.com> From: Robin Murphy Message-ID: Date: Wed, 3 Apr 2019 14:58:28 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.1 MIME-Version: 1.0 In-Reply-To: <1554265806-11501-7-git-send-email-anshuman.khandual@arm.com> Content-Type: text/plain; charset=utf-8; format=flowed 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: [ +Dan, Jerome ] On 03/04/2019 05:30, Anshuman Khandual wrote: > Arch implementation for functions which create or destroy vmemmap mapping > (vmemmap_populate, vmemmap_free) can comprehend and allocate from inside > device memory range through driver provided vmem_altmap structure which > fulfils all requirements to enable ZONE_DEVICE on the platform. Hence just ZONE_DEVICE is about more than just altmap support, no? > enable ZONE_DEVICE by subscribing to ARCH_HAS_ZONE_DEVICE. But this is only > applicable for ARM64_4K_PAGES (ARM64_SWAPPER_USES_SECTION_MAPS) only which > creates vmemmap section mappings and utilize vmem_altmap structure. What prevents it from working with other page sizes? One of the foremost use-cases for our 52-bit VA/PA support is to enable mapping large quantities of persistent memory, so we really do need this for 64K pages too. FWIW, it appears not to be an issue for PowerPC. > Signed-off-by: Anshuman Khandual > --- > arch/arm64/Kconfig | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index db3e625..b5d8cf5 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -31,6 +31,7 @@ config ARM64 > select ARCH_HAS_SYSCALL_WRAPPER > select ARCH_HAS_TEARDOWN_DMA_OPS if IOMMU_SUPPORT > select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST > + select ARCH_HAS_ZONE_DEVICE if ARM64_4K_PAGES IIRC certain configurations (HMM?) don't even build if you just turn this on alone (although of course things may have changed elsewhere in the meantime) - crucially, though, from previous discussions[1] it seems fundamentally unsafe, since I don't think we can guarantee that nobody will touch the corners of ZONE_DEVICE that also require pte_devmap in order not to go subtly wrong. I did get as far as cooking up some patches to sort that out [2][3] which I never got round to posting for their own sake, so please consider picking those up as part of this series. Robin. > select ARCH_HAVE_NMI_SAFE_CMPXCHG > select ARCH_INLINE_READ_LOCK if !PREEMPT > select ARCH_INLINE_READ_LOCK_BH if !PREEMPT > [1] https://lore.kernel.org/linux-mm/CAA9_cmfA9GS+1M1aSyv1ty5jKY3iho3CERhnRAruWJW3PfmpgA@mail.gmail.com/#t [2] http://linux-arm.org/git?p=linux-rm.git;a=commitdiff;h=61816b833afdb56b49c2e58f5289ae18809e5d67 [3] http://linux-arm.org/git?p=linux-rm.git;a=commitdiff;h=a5a16560eb1becf9a1d4cc0d03d6b5e76da4f4e1 (apologies to anyone if the linux-arm.org server is being flaky as usual and requires a few tries to respond properly)