From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alex Williamson Subject: Re: [Qemu-devel] [PATCH 28/35] kvm: x86: Introduce kvmclock device to save/restore its state Date: Tue, 18 Jan 2011 10:02:33 -0700 Message-ID: <1295370153.30628.10.camel@x201> 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> <4D35B7C6.7080204@siemens.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: Anthony Liguori , Avi Kivity , Markus Armbruster , Marcelo Tosatti , Glauber Costa , "kvm@vger.kernel.org" , "qemu-devel@nongnu.org" To: Jan Kiszka Return-path: Received: from mx1.redhat.com ([209.132.183.28]:6781 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752530Ab1ARRCk (ORCPT ); Tue, 18 Jan 2011 12:02:40 -0500 In-Reply-To: <4D35B7C6.7080204@siemens.com> Sender: kvm-owner@vger.kernel.org List-ID: On Tue, 2011-01-18 at 16:54 +0100, Jan Kiszka wrote: > 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. We abstract this through the msi/msix layer though, so the vfio driver doesn't directly know anything about kvm_state. Alex From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=52988 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1PfEzP-00070C-Ql for qemu-devel@nongnu.org; Tue, 18 Jan 2011 12:07:24 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1PfEx5-00038f-6R for qemu-devel@nongnu.org; Tue, 18 Jan 2011 12:04:57 -0500 Received: from mx1.redhat.com ([209.132.183.28]:33003) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1PfEx4-00038Y-Vq for qemu-devel@nongnu.org; Tue, 18 Jan 2011 12:02:39 -0500 Subject: Re: [Qemu-devel] [PATCH 28/35] kvm: x86: Introduce kvmclock device to save/restore its state From: Alex Williamson In-Reply-To: <4D35B7C6.7080204@siemens.com> 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> <4D35B7C6.7080204@siemens.com> Content-Type: text/plain; charset="UTF-8" Date: Tue, 18 Jan 2011 10:02:33 -0700 Message-ID: <1295370153.30628.10.camel@x201> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Jan Kiszka Cc: "kvm@vger.kernel.org" , Glauber Costa , Marcelo Tosatti , Markus Armbruster , "qemu-devel@nongnu.org" , Anthony Liguori , Avi Kivity On Tue, 2011-01-18 at 16:54 +0100, Jan Kiszka wrote: > 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. We abstract this through the msi/msix layer though, so the vfio driver doesn't directly know anything about kvm_state. Alex