From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id AC0C07C for ; Fri, 19 May 2023 12:41:23 +0000 (UTC) Received: by verein.lst.de (Postfix, from userid 2407) id A400368C7B; Fri, 19 May 2023 14:41:18 +0200 (CEST) Date: Fri, 19 May 2023 14:41:18 +0200 From: Christoph Hellwig To: Marek =?iso-8859-1?Q?Marczykowski-G=F3recki?= Cc: Christoph Hellwig , Juergen Gross , Stefano Stabellini , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Ben Skeggs , Karol Herbst , Lyude Paul , xen-devel@lists.xenproject.org, iommu@lists.linux.dev, linux-kernel@vger.kernel.org, nouveau@lists.freedesktop.org Subject: Re: [PATCH 2/4] x86: always initialize xen-swiotlb when xen-pcifront is enabling Message-ID: <20230519124118.GA5869@lst.de> References: <20230518134253.909623-1-hch@lst.de> <20230518134253.909623-3-hch@lst.de> <20230519040405.GA10818@lst.de> Precedence: bulk X-Mailing-List: iommu@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: 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/1.5.17 (2007-11-01) On Fri, May 19, 2023 at 12:10:26PM +0200, Marek Marczykowski-Górecki wrote: > While I would say PCI passthrough is not very common for PV guests, can > the decision about xen-swiotlb be delayed until you can enumerate > xenstore to check if there are any PCI devices connected (and not > allocate xen-swiotlb by default if there are none)? This would > still not cover the hotplug case (in which case, you'd need to force it > with a cmdline), but at least you wouldn't loose much memory just > because one of your VMs may use PCI passthrough (so, you have it enabled > in your kernel). How early can we query xenstore? We'd need to do this before setting up DMA for any device. The alternative would be to finally merge swiotlb-xen into swiotlb, in which case we might be able to do this later. Let me see what I can do there. 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 gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (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 E90E5C77B7F for ; Fri, 19 May 2023 12:41:25 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 736E410E0F2; Fri, 19 May 2023 12:41:25 +0000 (UTC) Received: from verein.lst.de (verein.lst.de [213.95.11.211]) by gabe.freedesktop.org (Postfix) with ESMTPS id C8F8A10E0F2 for ; Fri, 19 May 2023 12:41:23 +0000 (UTC) Received: by verein.lst.de (Postfix, from userid 2407) id A400368C7B; Fri, 19 May 2023 14:41:18 +0200 (CEST) Date: Fri, 19 May 2023 14:41:18 +0200 From: Christoph Hellwig To: Marek =?iso-8859-1?Q?Marczykowski-G=F3recki?= Message-ID: <20230519124118.GA5869@lst.de> References: <20230518134253.909623-1-hch@lst.de> <20230518134253.909623-3-hch@lst.de> <20230519040405.GA10818@lst.de> 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/1.5.17 (2007-11-01) Subject: Re: [Nouveau] [PATCH 2/4] x86: always initialize xen-swiotlb when xen-pcifront is enabling X-BeenThere: nouveau@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Nouveau development list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Juergen Gross , Stefano Stabellini , nouveau@lists.freedesktop.org, Dave Hansen , x86@kernel.org, linux-kernel@vger.kernel.org, iommu@lists.linux.dev, Ingo Molnar , Borislav Petkov , Ben Skeggs , "H. Peter Anvin" , xen-devel@lists.xenproject.org, Thomas Gleixner , Christoph Hellwig Errors-To: nouveau-bounces@lists.freedesktop.org Sender: "Nouveau" On Fri, May 19, 2023 at 12:10:26PM +0200, Marek Marczykowski-Górecki wrote: > While I would say PCI passthrough is not very common for PV guests, can > the decision about xen-swiotlb be delayed until you can enumerate > xenstore to check if there are any PCI devices connected (and not > allocate xen-swiotlb by default if there are none)? This would > still not cover the hotplug case (in which case, you'd need to force it > with a cmdline), but at least you wouldn't loose much memory just > because one of your VMs may use PCI passthrough (so, you have it enabled > in your kernel). How early can we query xenstore? We'd need to do this before setting up DMA for any device. The alternative would be to finally merge swiotlb-xen into swiotlb, in which case we might be able to do this later. Let me see what I can do there.