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[209.132.183.28]) by mx.google.com with ESMTPS id 8si1109011qtt.203.2019.04.03.09.07.33 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 03 Apr 2019 09:07:34 -0700 (PDT) Received-SPF: pass (google.com: domain of jglisse@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of jglisse@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=jglisse@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 478CB88AAE; Wed, 3 Apr 2019 16:07:31 +0000 (UTC) Received: from redhat.com (ovpn-125-190.rdu2.redhat.com [10.10.125.190]) by smtp.corp.redhat.com (Postfix) with ESMTPS id AF99B608A5; Wed, 3 Apr 2019 16:07:24 +0000 (UTC) Date: Wed, 3 Apr 2019 12:07:22 -0400 From: Jerome Glisse To: Robin Murphy Cc: 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, 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 Subject: Re: [PATCH 6/6] arm64/mm: Enable ZONE_DEVICE Message-ID: <20190403160722.GB12818@redhat.com> References: <1554265806-11501-1-git-send-email-anshuman.khandual@arm.com> <1554265806-11501-7-git-send-email-anshuman.khandual@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.26]); Wed, 03 Apr 2019 16:07:32 +0000 (UTC) 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 Wed, Apr 03, 2019 at 02:58:28PM +0100, Robin Murphy wrote: > [ +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. Correct _do not_ enable ZONE_DEVICE without support for pte_devmap detection. If you want some feature of ZONE_DEVICE. Like HMM as while DAX does require pte_devmap, HMM device private does not. So you would first have to split ZONE_DEVICE into more sub-features kconfig option. What is the end use case you are looking for ? Persistent memory ? Cheers, Jérôme