From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 212EBFEEF49 for ; Tue, 7 Apr 2026 14:44:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=F+uI6OTjdNGqztBt0n2prscGZ7Rv6C1epHgWbD05+lg=; b=eATp1eLZSrLhtQKEHyAknjGkvI 2AHACKmpNaC/9BQOrRr7mrR29f+L8rtHUXz7ncSuwSYscBqe+CpvKoVmMlgoiEBfB/PSVIhm8JXZ1 /nTw8W+CEgZIy7BQ6s4dVTGPKck6ksYtPoEoPpXqMQ9ySXny9MVb+X3GSPmC+nMBiFRkKfj8/xGHC HWLqe43Zh/jKXBss8wWmZymvwnlsm2KcbqwcKuepaAMDarx72lHIqqUe4z21Qrr3tx6xc+BGQpUID ji/bTvm7feeIumWkdAE9ADXGQPBbBknmKgW9XJij2+oRfgSPAcGWDCY/Vu73z3mGymeFODiaF/aha ph7iaHhA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1wA7f3-00000006e0u-2kiT; Tue, 07 Apr 2026 14:44:13 +0000 Received: from sea.source.kernel.org ([2600:3c0a:e001:78e:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1wA7f1-00000006dzy-14tk for linux-arm-kernel@lists.infradead.org; Tue, 07 Apr 2026 14:44:12 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id A400C44434; Tue, 7 Apr 2026 14:44:10 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 87D83C2BCAF; Tue, 7 Apr 2026 14:44:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1775573050; bh=IS0Hw9PqtMklbf3GWeAwTjwZLCZcdU9hKiZ7Q2p69rA=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=OPk/0Wse1jxxBZKtv4rcO4Gjx1K+m0MTWP/fTlIwRk1JwHS+5ZAVzLxPrI80dbo7S bt42fl7CaU2LebeROiJebJpvN6ACCEpKFDwoIoilQb7M1A9OPTbmptpMDPXx8/RTgA 0aGA+Q5EKLfGNjU0Reaccn6RVpk6KBg2/RfsPEMBiJl6v4M640lUVetpk/JyU6fHji saeKf5dKKqTxmKbyTaXTlSKhX5kABP9Jyhd6bHtOYPgcRiJePsej+US5fQhmP6cNbm eh1go172haGbqz7uIwADtg1yKxzB6OJBSGyXu+KDC9uTDa/IptojjpyCMl9x3acQhS kvl1pKU0QUmrw== Message-ID: Date: Tue, 7 Apr 2026 16:44:04 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC V1 00/16] arm64/mm: Enable 128 bit page table entries To: Anshuman Khandual , linux-arm-kernel@lists.infradead.org Cc: Catalin Marinas , Will Deacon , Ryan Roberts , Mark Rutland , Lorenzo Stoakes , Andrew Morton , Mike Rapoport , Linu Cherian , linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20260224051153.3150613-1-anshuman.khandual@arm.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260407_074411_341363_4D480D6F X-CRM114-Status: GOOD ( 17.94 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2/24/26 06:11, Anshuman Khandual wrote: > FEAT_D128 is a new arm architecture feature adding support for VMSAv9-128 > translation system. FEAT_D128 is an optional feature from ARMV9.3 onwards. > So with this feature arm64 platforms could have two different translation > systems, VMSAv8-64 and VMSAv9-128 could selectively be enabled. > > FEAT_D128 adds 128 bit page table entries, thus supporting larger physical > and virtual address range while also expanding available room for more MMU > management feature bits both for HW and SW. > > This series has been split into two parts. Generic MM changes followed by > arm64 platform changes, finally enabling D128 with a new config ARM64_D128. > > READ_ONCE() on page table entries get routed via level specific pxdp_get() > helpers which platforms could then override when required. These accessors > on arm64 platform help in ensuring page table accesses are performed in an > atomic manner while reading 128 bit page table entries. > > All ARM64_VA_BITS and ARM64_PA_BITS combinations for all page sizes are now > supported both on D64 and D128 translation regimes. Although new 56 bits VA > space is not yet supported. Similarly FEAT_D128 skip level is not supported > currently. > > Basic page table geometry has been changed with D128 as there are now fewer > entries per level. Please refer to the following table for leaf entry sizes > > D64 D128 > ------------------------------------------------ > | PAGE_SIZE | PMD | PUD | PMD | PUD | > -----------------------------|-----------------| > | 4K | 2M | 1G | 1M | 256M | > | 16K | 32M | 64G | 16M | 16G | > | 64K | 512M | 4T | 256M | 1T | > ------------------------------------------------ > Interesting. That means user space will have it even harder to optimize for THP sizes. What's the effect on cont-pte? Do they still span the same number of entries and there is effectively no change? > From arm64 kernel features perspective KVM, KASAN and UNMAP_KERNEL_AT_EL0 > are currently not supported as well. > > Open Questions: > > - Do we need to support UNMAP_KERNEL_AT_EL0 with D128 > - Do we need to emulate traditional D64 sizes at PUD, PMD level with D128 It would certainly make user space interaction easier. But then, user space already has to consider various PMD sizes (and is better of querying /sys/kernel/mm/transparent_hugepage/hpage_pmd_size instead of hardcoding it). s390x, for example, also has 1M PMD size. I guess with "emulating" you mean something simple like always allocating order-1 page tables that effectively have the same number of page table entries? The would be an option, but I recall that the pte_map_* infrastructure currently expects that leaf page tables only ever span a single page. So it wouldn't really give us a lot of easy benefit I guess. -- Cheers, David