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 X-Spam-Level: X-Spam-Status: No, score=-3.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 214AFC4363A for ; Wed, 28 Oct 2020 11:32:06 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id 20E5E246C6 for ; Wed, 28 Oct 2020 11:32:04 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="NDtZF3tW" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 20E5E246C6 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:60236 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kXjgR-0007u1-Lc for qemu-devel@archiver.kernel.org; Wed, 28 Oct 2020 07:32:03 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:49840) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kXjfa-0007J9-Mw for qemu-devel@nongnu.org; Wed, 28 Oct 2020 07:31:10 -0400 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:46835) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kXjfW-0004mh-UT for qemu-devel@nongnu.org; Wed, 28 Oct 2020 07:31:10 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1603884661; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=35+8XpEhiBzAcqTRMxXgOAJkP51u07bMPpxjJhHGR+o=; b=NDtZF3tW3Ic/Elwy6Z5iMMxOrqmCQNRUL33i/lQhuJf1/+o0pR4AP53bPV4wsQC3wmTX7/ Zq6SdkILUQPAwcPdyBEKxK3dY5/QieTG8vXoup+ok1dZFNg3bciTeyQlPNFxixSzdtE8nb bcAdH+RQZK5dO1YXBJWJyL4USi1FWhc= Received: from mail-wm1-f70.google.com (mail-wm1-f70.google.com [209.85.128.70]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-532-CY1QtzXVPnuFvFvsmaSARg-1; Wed, 28 Oct 2020 07:31:00 -0400 X-MC-Unique: CY1QtzXVPnuFvFvsmaSARg-1 Received: by mail-wm1-f70.google.com with SMTP id l17so889026wmb.0 for ; Wed, 28 Oct 2020 04:31:00 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=35+8XpEhiBzAcqTRMxXgOAJkP51u07bMPpxjJhHGR+o=; b=PL5OJg3x5rxTvnsDsBRsh5m/KaCI6l9Io60lpVgVKtK+pcMThKuPPGVwdBmxNOUdNv x0Zo8vxtBrLqAFwLVpa4D70qBXmR9t0aX9vZmaYJMZxIOJIDaiIv8+JLTFrG8j3w3vjJ ikic1NqZcxEij6fpMpfS8FEl1lK9+5E3qpLe6/ynIqiCTprY+4I75OhR6T/bDmVdMaFn Jl+13qaQmpC5pZv+mVYK62l+3kKN9LW9XnJRAGnBWaN9He3AiIqQOBZIYl6/O43ZZ2cc dwvrZNWpFl/WJEHWeE10BPinaAKNrKjjmM8J6fP5kiM0xl/VtYWj+xblIPMOfhQ2axnt Ahwg== X-Gm-Message-State: AOAM532y8fuNlThFswNOQnpijT5oZHIWQ9+BdKJeOfRydjmMcNRSD4dZ fCusqiNlRemNsgijPAuAwV2ZoYvSnog23HWjTsrlizF+XraD0QuCVMx7a1M0pu0pOq8KwtzMh40 3yi7NG3XCMr3WXng= X-Received: by 2002:a7b:cb8d:: with SMTP id m13mr7612234wmi.59.1603884659045; Wed, 28 Oct 2020 04:30:59 -0700 (PDT) X-Google-Smtp-Source: ABdhPJyoDvij9vpE30FEKkrHffWg6Hreb91GhghNA0FMar7kxEHU5fWzHxyGj+FCYllhH9eMZ8BlGA== X-Received: by 2002:a7b:cb8d:: with SMTP id m13mr7612205wmi.59.1603884658859; Wed, 28 Oct 2020 04:30:58 -0700 (PDT) Received: from redhat.com (bzq-79-176-118-93.red.bezeqint.net. [79.176.118.93]) by smtp.gmail.com with ESMTPSA id t5sm7123624wrb.21.2020.10.28.04.30.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 28 Oct 2020 04:30:58 -0700 (PDT) Date: Wed, 28 Oct 2020 07:30:55 -0400 From: "Michael S. Tsirkin" To: Stefan Hajnoczi Subject: Re: [PATCH] virtio: skip guest index check on device load Message-ID: <20201028072812-mutt-send-email-mst@kernel.org> References: <20201026151328.77611-1-felipe@nutanix.com> <20201027113049.GH79063@stefanha-x1.localdomain> <20201027082337-mutt-send-email-mst@kernel.org> <12146644-5D22-4CAC-9B4F-F16E84ED56AE@nutanix.com> <20201027085447-mutt-send-email-mst@kernel.org> <20201027090420-mutt-send-email-mst@kernel.org> <20201028110038.GE221115@stefanha-x1.localdomain> MIME-Version: 1.0 In-Reply-To: <20201028110038.GE221115@stefanha-x1.localdomain> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mst@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=63.128.21.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/10/28 01:51:10 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Paolo Bonzini , Jason Wang , "qemu-devel@nongnu.org" , Markus Armbruster , Felipe Franciosi Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Oct 28, 2020 at 11:00:38AM +0000, Stefan Hajnoczi wrote: > On Tue, Oct 27, 2020 at 09:04:46AM -0400, Michael S. Tsirkin wrote: > > It's not a waste of time, it's just a lot of work > > within guests. > > Luckily it does no harm to set the NEEDS_RESET bit even if the guest > doesn't handle it. > > If the guest driver is unaware it may continue to submit requests to the > device for a while. The device emulation code stops accepting new > requests though. This means the device will become unresponsive until > reset, which is not ideal but okay in the case where the device was put > into an invalid state. There is no actual rule that device must stop processing requests. Driver can only assume that is the case after it started the actual reset. > I agree that supporting NEEDS_RESET transparently inside guests is > difficult. The driver needs to reset and resume the device without > reporting errors to applications. In some cases drivers may not have > enough state in order to do that. It's also tricky to test all code > paths. I guess this is why no one has done it: drivers shouldn't enter > the NEEDS_RESET state anyway and handling it is complex. > > Stefan