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Fri, 07 Feb 2025 05:32:08 -0500 X-MC-Unique: WWoMm5FXPCeMH1TCHjxWqw-1 X-Mimecast-MFC-AGG-ID: WWoMm5FXPCeMH1TCHjxWqw Received: from mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.15]) (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-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 600FB1800876; Fri, 7 Feb 2025 10:32:06 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.56]) by mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 8EB561955F1B; Fri, 7 Feb 2025 10:31:55 +0000 (UTC) Date: Fri, 7 Feb 2025 10:31:51 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Shameerali Kolothum Thodi Cc: Nicolin Chen , Jason Gunthorpe , "qemu-arm@nongnu.org" , "qemu-devel@nongnu.org" , "eric.auger@redhat.com" , "peter.maydell@linaro.org" , "ddutile@redhat.com" , Linuxarm , "Wangzhou (B)" , jiangkunkun , Jonathan Cameron , "zhangfei.gao@linaro.org" , "nathanc@nvidia.com" Subject: Re: [RFC PATCH 0/5] hw/arm/virt: Add support for user-creatable nested SMMUv3 Message-ID: References: <20250206174647.GA3480821@nvidia.com> <20250206175843.GI2960738@nvidia.com> <13b1d8b97a314cb28b87563fa9b45299@huawei.com> <20250206181306.GK2960738@nvidia.com> <02a0080a4a1642d69b7f5dd4707a5b3d@huawei.com> <20250206182201.GL2960738@nvidia.com> <9112ba0694bd42199e279e37fbfc9dd0@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <9112ba0694bd42199e279e37fbfc9dd0@huawei.com> User-Agent: Mutt/2.2.13 (2024-03-09) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.15 Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com 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_H2=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham 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+alex.bennee=linaro.org@nongnu.org Sender: qemu-arm-bounces+alex.bennee=linaro.org@nongnu.org X-TUID: gSgYMGJTZrAa On Fri, Feb 07, 2025 at 10:21:17AM +0000, Shameerali Kolothum Thodi wrote: > > > > -----Original Message----- > > From: Nicolin Chen > > Sent: Thursday, February 6, 2025 8:33 PM > > To: Shameerali Kolothum Thodi > > ; Daniel P. Berrangé > > ; Jason Gunthorpe > > Cc: qemu-arm@nongnu.org; qemu-devel@nongnu.org; > > eric.auger@redhat.com; peter.maydell@linaro.org; ddutile@redhat.com; > > Linuxarm ; Wangzhou (B) > > ; jiangkunkun ; > > Jonathan Cameron ; > > zhangfei.gao@linaro.org; nathanc@nvidia.com > > Subject: Re: [RFC PATCH 0/5] hw/arm/virt: Add support for user-creatable > > nested SMMUv3 > > > > On Thu, Feb 06, 2025 at 02:22:01PM -0400, Jason Gunthorpe wrote: > > > On Thu, Feb 06, 2025 at 06:18:14PM +0000, Shameerali Kolothum Thodi > > wrote: > > > > > > > > So even if you invent an iommu ID we cannot accept it as a handle to > > > > > create viommu in iommufd. > > > > > > > > Creating the vIOMMU only happens when the user does a cold/hot > > plug of > > > > a VFIO device. At that time Qemu checks whether the assigned id > > matches > > > > with whatever the kernel tell it. > > > > > > This is not hard up until the guest is started. If you boot a guest > > > without a backing viommu iommufd object then there will be some more > > > complexities. > > > > Yea, I imagined that things would be complicated with hotplugs.. > > > > On one hand, I got the part that we need some fixed link forehand > > to ease migration/hotplugs. > > > > On the other hand, all IOMMUFD ioctls need a VFIO device FD, which > > brings the immediate attention that we cannot even decide vSMMU's > > capabilities being reflected in its IDR/IIDR registers, without a > > coldplug device -- if we boot a VM (one vSMMU<->pSMMU) with only a > > hotplug device, the IOMMU_GET_HW_INFO cannot be done during guest > > Right. I forgot about the call to smmu_dev_get_info() during the reset. > That means we need at least one dev per Guest SMMU during Guest > boot :( That's pretty unpleasant as a usage restriction. It sounds like there needs to be a way to configure & control the vIOMMU independantly of attaching a specific VFIO device. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|