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 2AB9CC982D0 for ; Thu, 17 Sep 2026 18:28:26 +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=b5zVLhEkKOWEwakOfls77zzn3VcbclTffxYn4L85i8c=; b=GXIbUHNolLWlsqoAtfTP6M/tNO FPt2Hn7Hw0Oox5FEQyjj5svip0HcpG6j/gDNrZK6jBxH/2KEroCL+Ui7mbE+/zHFJ0wbQGE+E0k3Y iH6sCnUa4dpu5L6jmKiwZACyQD6itYj/ax7pCzxzcWrWIiGB+bLFNc3hcS5mShyY6hkjXZR1p0woo duvrRFkC45OMSP33GKjaqdemOhc2xThiXWhJKKVoGHZEb5jxeubhrwEjZx9zaZc/SLhGgtWAweoWK qbXS5DIGTc6ipq1VPq7QfISE0h4u1KtukO4g8Vx6vqyRJAFFwKajhzA6bxWi7F5FVD3fbIUPpnbeA MzinJZHA==; 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charset=UTF-8 Content-Transfer-Encoding: 7bit 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 9/17/26 08:18, Anshuman Khandual wrote: > On Wed, Sep 16, 2026 at 04:30:05PM +0200, David Hildenbrand (Arm) wrote: >> On 9/7/26 05:50, Anshuman Khandual wrote: >>> FEAT_D128 halves PTRS_PER_PXX thus shrinking the VA range coverage >>> for each page table level. Hence in order to preserve all existing >>> VA range configurations, some geometry now need to become 5-level. >>> >> >> Hmm, wasn't this 5-levels before, but other code allocated+initialized the p4d >> table for us? > > But fixmap was never 5 level earlier. I mean the page table hierarchy. It's confusing. > >> >> I mean, I see how we are filling in another level, but I don't see how we would >> reconfigure something to use 5 page table levels? > > IIUC existing configurations which never required 5 levels would not need > this reconfiguration even now. We only map a handful of MB into a single leaf page table. The only reason why we have to install more page tables into upper levels is because they were not instantiated by other code. > >> >>> Since fixmap is used to build and manipulate page tables early on >>> during boot the mapping must also gain that additional level which >>> was not required earlier. >> >> I am no expert ... but I am confused :) >> >> We do have a loop only in early_fixmap_init_pmd(). So we cannot possibly span >> more than a single ... PTE table? >> >>> >>> Enable fixmap with 5 level page table when required. This creates table >>> entries at the PGD level. Add a fallback stub for pgd_page_paddr() when >>> (PGTBALE_LEVELS <= 4) which helps in intercepting any unintended usage. >> >> >> Again, I am very confused. Is it really just "As the page table layout changes, >> we might no longer have a p4d table pre-populated for the range our fixmap falls >> into. So if there is no p4d table yet, populate a static one just like we do for >> the other levels." > > Right. Best to rewrite the patch description along these lines. -- Cheers, David