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 lists1p.gnu.org (lists1p.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 EC95BCD8C92 for ; Mon, 8 Jun 2026 08:56:07 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1wWVlt-00016b-2f; Mon, 08 Jun 2026 04:55:49 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wWVlp-00015k-B1 for qemu-arm@nongnu.org; Mon, 08 Jun 2026 04:55:45 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wWVlm-0001Mz-I9 for qemu-arm@nongnu.org; Mon, 08 Jun 2026 04:55:43 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1780908939; h=from:from:reply-to: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=2oSkTdQLECK9diOUg2NKmtmz1IKvhAZdLEXS7Xs1mn8=; b=CnLQHPKYrO4lbmONjV90hOXbcqWySg/jpo0ThsBIqv+zkjKEVRAIx0QRqlcpWv1fzKZEFq 72VNEG4S/ePYNcbe4dvp/O81qzoUqkECuOskzTi0Hvl7y9gOTzXDpM0MoVXNHcrA9bzqza X1igBk7GrwV4l10FusRXWdvMEOVrGZM= Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-101-ec9_myasPGC-NtiFNk8EUg-1; Mon, 08 Jun 2026 04:55:35 -0400 X-MC-Unique: ec9_myasPGC-NtiFNk8EUg-1 X-Mimecast-MFC-AGG-ID: ec9_myasPGC-NtiFNk8EUg_1780908935 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id C34F71956094; Mon, 8 Jun 2026 08:55:34 +0000 (UTC) Received: from redhat.com (unknown [10.44.49.219]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 7D6C81955DC9; Mon, 8 Jun 2026 08:55:32 +0000 (UTC) Date: Mon, 8 Jun 2026 09:55:28 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Gavin Shan Cc: qemu-devel@nongnu.org, qemu-arm@nongnu.org, mst@redhat.com, jugraham@redhat.com, shan.gavin@gmail.com Subject: Re: [PATCH RFCv1] virtio: Inherit max bounce buffer size from bus parent if possible Message-ID: References: <20260608001821.850921-1-gshan@redhat.com> MIME-Version: 1.0 In-Reply-To: <20260608001821.850921-1-gshan@redhat.com> User-Agent: Mutt/2.3.2 (2026-04-26) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 X-Mimecast-MFC-PROC-ID: vPRKe_tY_TClhQmb7jIY7EdVNRFtkkqCqBZyOxGeLaE_1780908935 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: 8 X-Spam_score: 0.8 X-Spam_bar: / X-Spam_report: (0.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.445, 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_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_SBL_CSS=3.335, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-arm@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-arm-bounces+qemu-arm=archiver.kernel.org@nongnu.org Sender: qemu-arm-bounces+qemu-arm=archiver.kernel.org@nongnu.org On Mon, Jun 08, 2026 at 10:18:21AM +1000, Gavin Shan wrote: > On the guest where a NVidia's GH100 card is passed from the host, the > guest system hang can be observed on attempt to compile 'cuda-samples', > as reported by Julia. snip > By default, the max bounce buffer size is only 4096 bytes, even less > than one page when the guest page is 64KB. This tries to fix the issue > by inheriting the customized max bounce buffer size of the virtio bus's > parent through property 'x-max-bounce-buffer-size' when the customized > size is a larger one. With this applied, no guest system hang is seen > with '-device virtio-blk-pci,...,x-max-bounce-buffer-size=268435456'. "x-max-bounce-buffer-size" is an experimental / unsupported property. We really shouldn't be expecting users to have to set this in a production deployment in order to stop a guest from hanging. Even if we dropped the experimental marker from this property, users would still need to know to provide this magic setting, so it would still be broken out of the box. How can we get a solution that "just works" out of the box, which is fully supported, not relying on experimental properties ? > > Reported-by: Julia Graham > Signed-off-by: Gavin Shan > --- > hw/virtio/virtio-bus.c | 14 ++++++++++++++ > 1 file changed, 14 insertions(+) With regards, Daniel -- |: https://berrange.com ~~ https://hachyderm.io/@berrange :| |: https://libvirt.org ~~ https://entangle-photo.org :| |: https://pixelfed.art/berrange ~~ https://fstop138.berrange.com :|