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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 28E16C0032E for ; Wed, 25 Oct 2023 17:11:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229743AbjJYRLc (ORCPT ); Wed, 25 Oct 2023 13:11:32 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54324 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229746AbjJYRLb (ORCPT ); Wed, 25 Oct 2023 13:11:31 -0400 Received: from bmailout3.hostsharing.net (bmailout3.hostsharing.net [IPv6:2a01:4f8:150:2161:1:b009:f23e:0]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 35C9A132 for ; Wed, 25 Oct 2023 10:11:28 -0700 (PDT) Received: from h08.hostsharing.net (h08.hostsharing.net [IPv6:2a01:37:1000::53df:5f1c:0]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256 client-signature RSA-PSS (4096 bits) client-digest SHA256) (Client CN "*.hostsharing.net", Issuer "RapidSSL Global TLS RSA4096 SHA256 2022 CA1" (verified OK)) by bmailout3.hostsharing.net (Postfix) with ESMTPS id C9FF210096662; Wed, 25 Oct 2023 19:11:26 +0200 (CEST) Received: by h08.hostsharing.net (Postfix, from userid 100393) id 8E1E4110AC; Wed, 25 Oct 2023 19:11:26 +0200 (CEST) Date: Wed, 25 Oct 2023 19:11:26 +0200 From: Lukas Wunner To: Logan Gunthorpe Cc: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= , Bjorn Helgaas , Simon Richter , 1015871@bugs.debian.org, linux-pci@vger.kernel.org, Alex Deucher , Krzysztof Wilczy??ski , Emanuele Rocca Subject: Re: Enabling PCI_P2PDMA for distro kernels? Message-ID: <20231025171126.GA9661@wunner.de> References: <20231025061927.smn5xnwpkasctpn7@pengutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On Wed, Oct 25, 2023 at 10:30:07AM -0600, Logan Gunthorpe wrote: > In addition to the above, P2PDMA transfers are only allowed by the > kernel for traffic that flows through certain host bridges that are > known to work. For AMD, all modern CPUs are on this list, but for Intel, > the list is very patchy. This has recently been brought up internally at Intel and nobody could understand why there's a whitelist in the first place. A long-time PCI architect told me that Intel silicon validation has been testing P2PDMA at least since the Lindenhurst days, i.e. since 2005. What's the reason for the whitelist? Was there Intel hardware which didn't support it or turned out to be broken? I imagine (but am not certain) that the feature might only be enabled for server SKUs, is that the reason? Thanks, Lukas