From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=52419 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1PfDii-00063Q-L9 for qemu-devel@nongnu.org; Tue, 18 Jan 2011 10:43:49 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1PfDid-0008Ia-Kj for qemu-devel@nongnu.org; Tue, 18 Jan 2011 10:43:40 -0500 Received: from thoth.sbs.de ([192.35.17.2]:21356) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1PfDid-0008Hv-Bq for qemu-devel@nongnu.org; Tue, 18 Jan 2011 10:43:39 -0500 Message-ID: <4D35B521.3090601@siemens.com> Date: Tue, 18 Jan 2011 16:43:29 +0100 From: Jan Kiszka MIME-Version: 1.0 Subject: Re: [Qemu-devel] [PATCH 28/35] kvm: x86: Introduce kvmclock device to save/restore its state References: <4D2B6CB5.9050602@codemonkey.ws> <4D2B74D8.4080309@web.de> <4D2B8662.9060909@web.de> <4D2C60FB.7030009@linux.vnet.ibm.com> <4D2D80ED.8030405@redhat.com> <4D2D82EE.20002@siemens.com> <4D35A39A.8000801@siemens.com> <4D35ABF8.9050700@linux.vnet.ibm.com> In-Reply-To: <4D35ABF8.9050700@linux.vnet.ibm.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Anthony Liguori Cc: "kvm@vger.kernel.org" , Glauber Costa , Marcelo Tosatti , "qemu-devel@nongnu.org" , Markus Armbruster , Avi Kivity On 2011-01-18 16:04, Anthony Liguori wrote: > On 01/18/2011 08:28 AM, Jan Kiszka wrote: >> On 2011-01-12 11:31, Jan Kiszka wrote: >> >>> Am 12.01.2011 11:22, Avi Kivity wrote: >>> >>>> On 01/11/2011 03:54 PM, Anthony Liguori wrote: >>>> >>>>> Right, we should introduce a KVMBus that KVM devices are created on. >>>>> The devices can get at KVMState through the BusState. >>>>> >>>> There is no kvm bus in a PC (I looked). We're bending the device model >>>> here because a device is implemented in the kernel and not in >>>> userspace. An implementation detail is magnified beyond all proportions. >>>> >>>> An ioapic that is implemented by kvm lives in exactly the same place >>>> that the qemu ioapic lives in. An assigned pci device lives on the PCI >>>> bus, not a KVMBus. If we need a pointer to KVMState, then we must find >>>> it elsewhere, not through creating imaginary buses that don't exist. >>>> >>>> >>> Exactly. >>> >>> So we can either "infect" the whole device tree with kvm (or maybe a >>> more generic accelerator structure that also deals with Xen) or we need >>> to pull the reference inside the device's init function from some global >>> service (kvm_get_state). >>> >> Note that this topic is still waiting for good suggestions, specifically >> from those who believe in kvm_state references :). This is not only >> blocking kvmstate merge but will affect KVM irqchips as well. >> >> It boils down to how we reasonably pass a kvm_state reference from >> machine init code to a sysbus device. I'm probably biased, but I don't >> see any way that does not work against the idea of confining access to >> kvm_state or breaks device instantiation from the command line or a >> config file. >> > > A KVM device should sit on a KVM specific bus that hangs off of sysbus. > It can get to kvm_state through that bus. > > That bus doesn't get instantiated through qdev so requiring a pointer > argument should not be an issue. > This design is in conflict with the requirement to attach KVM-assisted devices also to their home bus, e.g. an assigned PCI device to the PCI bus. We don't support multi-homed qdev devices. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux