From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=48671 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1PfDtV-0002YQ-9Z for qemu-devel@nongnu.org; Tue, 18 Jan 2011 10:54:54 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1PfDtT-000432-T4 for qemu-devel@nongnu.org; Tue, 18 Jan 2011 10:54:53 -0500 Received: from thoth.sbs.de ([192.35.17.2]:24056) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1PfDtT-00042v-Fy for qemu-devel@nongnu.org; Tue, 18 Jan 2011 10:54:51 -0500 Message-ID: <4D35B7C6.7080204@siemens.com> Date: Tue, 18 Jan 2011 16:54:46 +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> <4D35B521.3090601@siemens.com> <4D35B648.1070208@linux.vnet.ibm.com> In-Reply-To: <4D35B648.1070208@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 , Alex Williamson , Avi Kivity On 2011-01-18 16:48, Anthony Liguori wrote: > On 01/18/2011 09:43 AM, Jan Kiszka wrote: >> 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. >> > > With vfio, would an assigned PCI device even need kvm_state? IIUC: Yes, for establishing the irqfd link. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux