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 lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (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 BA342CA5FFC for ; Wed, 7 Oct 2026 16:14:35 +0000 (UTC) Received: from list by lists.xenproject.org with outflank-mailman.1442549.1660101 (Exim 4.92) (envelope-from ) id 1xEUHb-000302-QY; Wed, 07 Oct 2026 16:14:19 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 1442549.1660101; Wed, 07 Oct 2026 16:14:19 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1xEUHb-0002zu-NA; Wed, 07 Oct 2026 16:14:19 +0000 Received: by outflank-mailman (input) for mailman id 1442549; Wed, 07 Oct 2026 16:14:17 +0000 Received: from mail.xenproject.org ([104.130.215.37]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1xEUHZ-0002z0-U8 for xen-devel@lists.xenproject.org; Wed, 07 Oct 2026 16:14:17 +0000 Received: from xenbits.xenproject.org ([104.239.192.120]) by mail.xenproject.org with esmtp (Exim 4.96) (envelope-from ) id 1xEUHZ-001i6y-1O; Wed, 07 Oct 2026 16:14:17 +0000 Received: from 224.pool85-54-217.dynamic.orange.es ([85.54.217.224] helo=localhost) by xenbits.xenproject.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.96) (envelope-from ) id 1xEUHZ-003XMO-0L; Wed, 07 Oct 2026 16:14:17 +0000 X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=xenproject.org; s=20200302mail; h=In-Reply-To:Content-Transfer-Encoding: Content-Type:MIME-Version:References:Message-ID:Subject:Cc:To:From:Date; bh=wyyl9UAOzk73xXmM5mfnr7RlHBErYaRJAGrqdTLMHKY=; b=ojvH39jRu28XUEDTV2jPEHrKae Y7yuh4xZVCxvfeMTU4zdemzOiKFBkEuBHzUNfyLjSBDeAV3OrK6jQKm4BqqSaWUcsHEy6KASxds5J N2ctFcnl3ot/xM1Ix3gARC4SmEq5XE6BCBkqkb1+GF9N8nz2y6q7v4Cn+kfHzSt7sxaQ=; Date: Wed, 7 Oct 2026 18:14:15 +0200 From: Roger Pau =?utf-8?B?TW9ubsOp?= To: George Dunlap Cc: xen-devel@lists.xenproject.org, Roger Pau =?utf-8?B?TW9ubsOp?= , Jan Beulich , Andrew Cooper , Teddy Astie Subject: Re: [PATCH v3 04/18] x86/domain_page: drop redundant create_perdomain_mapping() call Message-ID: References: <20261007104051.48841-1-gwd@xenproject.org> <20261007104051.48841-5-gwd@xenproject.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20261007104051.48841-5-gwd@xenproject.org> On Wed, Oct 07, 2026 at 11:40:37AM +0100, George Dunlap wrote: > From: Roger Pau Monné > > We want to change per-domain mappings to be per-vCPU mappings. In > preparation for that, we want to arrange that > create_perdomain_mapping() work either with a single perdomain area, > or with a per-vCPU perdomain area. > > One of the current calls in a domain context turns out to be > unnecessary: > > mapcache_domain_init() pre-plumbs L1 tables over the whole > inuse/garbage bitmap range (sized for the full MAPCACHE_ENTRIES > capacity), without populating any data pages. The plumbing is > redundant: mapcache_vcpu_init() installs the bitmap pages the domain > will actually use with populating calls, which allocate any missing > page-table structure on demand -- and since d->max_vcpus is fixed > before any vCPU is created, the range those calls cover never grows. > The pre-plumbed tail beyond it backs virtual addresses that are never > populated at all. > > In debug builds, and on hosts with memory hotplug or with more memory > than the PV directmap covers, the call was also what first allocated a > PV domain's per-domain L3. Release builds on other hosts already > allocated it only with the first vCPU. > > Drop the call; now we always allocate only with the first vCPU. > > With the only fallible operation gone, mapcache_domain_init() becomes > void, and arch_domain_create()'s error handling for it goes away. > > The per-domain-mapping work in mapcache_vcpu_init() stays where it is > rather than moving into mapcache_domain_init() along with this change, > ready for a later patch which introduces per-vCPU mapcaches. > > Signed-off-by: Roger Pau Monné > Assisted-by: Claude Code:claude-fable-5, Claude Code:claude-opus-4-8, Claude Code:claude-opus-5-5 > Signed-off-by: George Dunlap Reviewed-by: Roger Pau Monné Thanks, Roger.