From patchwork Thu Nov 25 12:06:29 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Ani Sinha X-Patchwork-Id: 12638969 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.gnu.org (lists.gnu.org [209.51.188.17]) (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 041F9C433F5 for ; Thu, 25 Nov 2021 12:07:39 +0000 (UTC) Received: from localhost ([::1]:55178 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mqDXO-00010q-Q8 for qemu-devel@archiver.kernel.org; Thu, 25 Nov 2021 07:07:38 -0500 Received: from eggs.gnu.org ([209.51.188.92]:45142) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mqDWV-0000HD-EE for qemu-devel@nongnu.org; Thu, 25 Nov 2021 07:06:43 -0500 Received: from [2607:f8b0:4864:20::632] (port=46646 helo=mail-pl1-x632.google.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1mqDWT-0001Xw-Ek for qemu-devel@nongnu.org; Thu, 25 Nov 2021 07:06:43 -0500 Received: by mail-pl1-x632.google.com with SMTP id p18so4368456plf.13 for ; Thu, 25 Nov 2021 04:06:40 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=anisinha-ca.20210112.gappssmtp.com; s=20210112; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=o5WhSH/wfhxb1Ak6Trg+laOzpvY8CUsKlnhyXtDQzW4=; b=Jy0XWzeLmGP8+cU+8g9Ad85CS+0c+iGeN62IQgcieTRtg8phFR6VSGmv69K4StQWS9 RNH2s+VS/hbAOe8uaE/4Mva7QQvwag1hxKVPBHW37CjcMmpca+SOjB8Urxo9I5y07hU2 +a6mfc5YZOPwCtzp3zJKnbv9//v6vlzxkwN61CnmBNWgII2GESD8G8KVBR1eljle7ZmI J7dtNyRECzMSEiZbXp8HF9ZUJ/nwtAJrZUSalrqsLKrZ9vTnS4UeQgJG3bkK7v7navrV 80Gy0Dfh7u9/q/0BKRFa6QcpTIalIbLm4PEUWIpj2ovlhauWcAeAwVhcaTG1gghbkv9v 3igQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=o5WhSH/wfhxb1Ak6Trg+laOzpvY8CUsKlnhyXtDQzW4=; b=k/YHb7ysn9iWO0uEA0cyGf6AsiFzxBvkPKAdAzktqdtAxvnaQVGX16civgBMp9S3xM srBvfjc8LNxgtaXHutszeW+9WcQFFTAPbPIYD98nzzdYRtQuCn1G/q22+W5jmA01+tPW XYnSBMypJg4Bj4mgksa3anr5N5k10Psu0TWMupDCx2hDgiCl4LkJKgUIpCeietIfAjlS SXLv3X/ZqIScTX1zkYh/SqQlLVgmmCuiSCJsqq0YIONjZEniI0lPg1muQ5+pl5cWaH7R J2fdh1kEkEsBBMsfYI6OfzeTX8F+UeVd96sTWpLXkVfk1C6Qb5El0mdOol3W9v12Mgtt gatQ== X-Gm-Message-State: AOAM532fs+9qe+T/akmt5dpjEbe21WU+XCNaNCIT+u9Jv9nVn0hQT6z2 BNZ3Ak9G4sdyniAALulHhRXcTA== X-Google-Smtp-Source: ABdhPJzWmcYNDNX4YG6iZh66om5kn8hrG7DJWVX8vtVTsHSNxLMtP4mxOqcuBi0CnQ7Ttalq/aM+1A== X-Received: by 2002:a17:90a:7004:: with SMTP id f4mr6280531pjk.156.1637841999052; Thu, 25 Nov 2021 04:06:39 -0800 (PST) Received: from anisinha-lenovo.ba.nuagenetworks.net ([49.207.198.191]) by smtp.googlemail.com with ESMTPSA id nv12sm3212738pjb.49.2021.11.25.04.06.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 25 Nov 2021 04:06:38 -0800 (PST) From: Ani Sinha To: "Michael S. Tsirkin" , Marcel Apfelbaum Subject: [PATCH-for-6.2] docs: add a word of caution on x-native-hotplug property for pcie-root-ports Date: Thu, 25 Nov 2021 17:36:29 +0530 Message-Id: <20211125120629.187014-1-ani@anisinha.ca> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 X-Host-Lookup-Failed: Reverse DNS lookup failed for 2607:f8b0:4864:20::632 (failed) Received-SPF: none client-ip=2607:f8b0:4864:20::632; envelope-from=ani@anisinha.ca; helo=mail-pl1-x632.google.com X-Spam_score_int: -10 X-Spam_score: -1.1 X-Spam_bar: - X-Spam_report: (-1.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, PDS_HP_HELO_NORDNS=0.001, RCVD_IN_DNSWL_NONE=-0.0001, RDNS_NONE=0.793, SPF_HELO_NONE=0.001, SPF_NONE=0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Ani Sinha , imammedo@redhat.com, qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" x-native-hotplug property, when used in order to disable HPC bit on the PCIE root ports, can lead to unexpected results from the guest operating system. Users are strongly advised not to touch this property in order to manipulte the HPC bit. Add a word of caution in the pcie.txt doc file to document this. Signed-off-by: Ani Sinha --- docs/pcie.txt | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-) diff --git a/docs/pcie.txt b/docs/pcie.txt index 89e3502075..e1f99f725f 100644 --- a/docs/pcie.txt +++ b/docs/pcie.txt @@ -262,11 +262,26 @@ PCI Express Root Ports (and PCI Express Downstream Ports). Port, which may come handy for hot-plugging another device. -5.3 Hot-plug example: +5.2 Hot-plug example: Using HMP: (add -monitor stdio to QEMU command line) device_add ,id=,bus= +5.3 A word of caution using hotplug on PCI Express Root Ports: +Starting Qemu version 6.2, PCI Express Root ports have a property +"x-native-hotplug" ("native-hotplug" for Qemu version 6.1), that can be used to +enable or disable hotplug on that port. For example: + +-device pcie-root-port,x-native-hotplug=off,... etc. + +The "x-" prefix indicates that this property is highly experimental and can +lead to unexpected results from the guest operating system if users try to use +it to alter the native hotplug on the port. It also means that the property +name and its behavior is liable to change in the future and is not expected to +be stable across Qemu versions. Therefore, end users are advised not to change +the value of this option from its default set value or use it in the Qemu +command line. + 6. Device assignment ==================== Host devices are mostly PCI Express and should be plugged only into