From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:49635) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aVg2R-0003UR-P4 for qemu-devel@nongnu.org; Tue, 16 Feb 2016 08:51:37 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aVg2O-00049b-Ee for qemu-devel@nongnu.org; Tue, 16 Feb 2016 08:51:35 -0500 Received: from mx1.redhat.com ([209.132.183.28]:40196) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aVg2O-00049S-4i for qemu-devel@nongnu.org; Tue, 16 Feb 2016 08:51:32 -0500 Date: Tue, 16 Feb 2016 14:51:25 +0100 From: Igor Mammedov Message-ID: <20160216145125.7f12882f@nial.brq.redhat.com> In-Reply-To: <56C317E1.1020602@redhat.com> References: <20160128125842-mutt-send-email-mst@redhat.com> <20160128130316.11af4330@nial.brq.redhat.com> <20160128145348-mutt-send-email-mst@redhat.com> <20160129121359.17842fef@nial.brq.redhat.com> <20160131170118-mutt-send-email-mst@redhat.com> <20160202105953.476a05bd@nial.brq.redhat.com> <20160202123756-mutt-send-email-mst@redhat.com> <20160209114608.4f89b528@nial.brq.redhat.com> <20160209131656-mutt-send-email-mst@redhat.com> <20160211161605.0022ed38@nial.brq.redhat.com> <20160211180836-mutt-send-email-mst@redhat.com> <56C2F46D.4080907@redhat.com> <20160216131737.7df40a1d@nial.brq.redhat.com> <56C317E1.1020602@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v19 3/9] pc: add a Virtual Machine Generation ID device List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Marcel Apfelbaum Cc: Xiao Guangrong , ehabkost@redhat.com, Marcel Apfelbaum , ghammer@redhat.com, "Michael S. Tsirkin" , qemu-devel@nongnu.org, lcapitulino@redhat.com, lersek@redhat.com On Tue, 16 Feb 2016 14:36:49 +0200 Marcel Apfelbaum wrote: > On 02/16/2016 02:17 PM, Igor Mammedov wrote: > > On Tue, 16 Feb 2016 12:05:33 +0200 > > Marcel Apfelbaum wrote: > > > >> On 02/11/2016 06:30 PM, Michael S. Tsirkin wrote: > >>> On Thu, Feb 11, 2016 at 04:16:05PM +0100, Igor Mammedov wrote: > >>>> On Tue, 9 Feb 2016 14:17:44 +0200 > >>>> "Michael S. Tsirkin" wrote: > >>>> > >>>>> On Tue, Feb 09, 2016 at 11:46:08AM +0100, Igor Mammedov wrote: > >>>>>>> So the linker interface solves this rather neatly: > >>>>>>> bios allocates memory, bios passes memory map to guest. > >>>>>>> Served us well for several years without need for extensions, > >>>>>>> and it does solve the VM GEN ID problem, even though > >>>>>>> 1. it was never designed for huge areas like nvdimm seems to want to use > >>>>>>> 2. we might want to add a new 64 bit flag to avoid touching low memory > >>>>>> linker interface is fine for some readonly data, like ACPI tables > >>>>>> especially fixed tables not so for AML ones is one wants to patch it. > >>>>>> > >>>>>> However now when you want to use it for other purposes you start > >>>>>> adding extensions and other guest->QEMU channels to communicate > >>>>>> patching info back. > >>>>>> It steals guest's memory which is also not nice and doesn't scale well. > >>>>> > >>>>> This is an argument I don't get. memory is memory. call it guest memory > >>>>> or RAM backed PCI BAR - same thing. MMIO is cheaper of course > >>>>> but much slower. > >>>>> > >>>>> ... > >>>> It however matters for user, he pays for guest with XXX RAM but gets less > >>>> than that. And that will be getting worse as a number of such devices > >>>> increases. > >>>> > >>>>>>> OK fine, but returning PCI BAR address to guest is wrong. > >>>>>>> How about reading it from ACPI then? Is it really > >>>>>>> broken unless there's *also* a driver? > >>>>>> I don't get question, MS Spec requires address (ADDR method), > >>>>>> and it's read by ACPI (AML). > >>>>> > >>>>> You were unhappy about DMA into guest memory. > >>>>> As a replacement for DMA, we could have AML read from > >>>>> e.g. PCI and write into RAM. > >>>>> This way we don't need to pass address to QEMU. > >>>> That sounds better as it saves us from allocation of IO port > >>>> and QEMU don't need to write into guest memory, the only question is > >>>> if PCI_Config opregion would work with driver-less PCI device. > >>> > >>> Or PCI BAR for that reason. I don't know for sure. > >>> > >>>> > >>>> And it's still pretty much not test-able since it would require > >>>> fully running OSPM to execute AML side. > >>> > >>> AML is not testable, but that's nothing new. > >>> You can test reading from PCI. > >>> > >>>>> > >>>>>> As for working PCI_Config OpRegion without driver, I haven't tried, > >>>>>> but I wouldn't be surprised if it doesn't, taking in account that > >>>>>> MS introduced _DSM doesn't. > >>>>>> > >>>>>>> > >>>>>>> > >>>>>>>>>> Just compare with a graphics card design, where on device memory > >>>>>>>>>> is mapped directly at some GPA not wasting RAM that guest could > >>>>>>>>>> use for other tasks. > >>>>>>>>> > >>>>>>>>> This might have been true 20 years ago. Most modern cards do DMA. > >>>>>>>> > >>>>>>>> Modern cards, with it's own RAM, map its VRAM in address space directly > >>>>>>>> and allow users use it (GEM API). So they do not waste conventional RAM. > >>>>>>>> For example NVIDIA VRAM is mapped as PCI BARs the same way like in this > >>>>>>>> series (even PCI class id is the same) > >>>>>>> > >>>>>>> Don't know enough about graphics really, I'm not sure how these are > >>>>>>> relevant. NICs and disks certainly do DMA. And virtio gl seems to > >>>>>>> mostly use guest RAM, not on card RAM. > >>>>>>> > >>>>>>>>>> VMGENID and NVDIMM use-cases look to me exactly the same, i.e. > >>>>>>>>>> instead of consuming guest's RAM they should be mapped at > >>>>>>>>>> some GPA and their memory accessed directly. > >>>>>>>>> > >>>>>>>>> VMGENID is tied to a spec that rather arbitrarily asks for a fixed > >>>>>>>>> address. This breaks the straight-forward approach of using a > >>>>>>>>> rebalanceable PCI BAR. > >>>>>>>> > >>>>>>>> For PCI rebalance to work on Windows, one has to provide working PCI driver > >>>>>>>> otherwise OS will ignore it when rebalancing happens and > >>>>>>>> might map something else over ignored BAR. > >>>>>>> > >>>>>>> Does it disable the BAR then? Or just move it elsewhere? > >>>>>> it doesn't, it just blindly ignores BARs existence and maps BAR of > >>>>>> another device with driver over it. > >>>>> > >>>>> Interesting. On classical PCI this is a forbidden configuration. > >>>>> Maybe we do something that confuses windows? > >>>>> Could you tell me how to reproduce this behaviour? > >>>> #cat > t << EOF > >>>> pci_update_mappings_del > >>>> pci_update_mappings_add > >>>> EOF > >>>> > >>>> #./x86_64-softmmu/qemu-system-x86_64 -snapshot -enable-kvm -snapshot \ > >>>> -monitor unix:/tmp/m,server,nowait -device pci-bridge,chassis_nr=1 \ > >>>> -boot menu=on -m 4G -trace events=t ws2012r2x64dc.img \ > >>>> -device ivshmem,id=foo,size=2M,shm,bus=pci.1,addr=01 > >>>> > >>>> wait till OS boots, note BARs programmed for ivshmem > >>>> in my case it was > >>>> 01:01.0 0,0xfe800000+0x100 > >>>> then execute script and watch pci_update_mappings* trace events > >>>> > >>>> # for i in $(seq 3 18); do printf -- "device_add e1000,bus=pci.1,addr=%x\n" $i | nc -U /tmp/m; sleep 5; done; > >>>> > >>>> hotplugging e1000,bus=pci.1,addr=12 triggers rebalancing where > >>>> Windows unmaps all BARs of nics on bridge but doesn't touch ivshmem > >>>> and then programs new BARs, where: > >>>> pci_update_mappings_add d=0x7fa02ff0cf90 01:11.0 0,0xfe800000+0x20000 > >>>> creates overlapping BAR with ivshmem > >>> > >>> > >>> Thanks! > >>> We need to figure this out because currently this does not > >>> work properly (or maybe it works, but merely by chance). > >>> Me and Marcel will play with this. > >>> > >> > >> I checked and indeed we have 2 separate problems: > >> > >> 1. ivshmem is declared as PCI RAM controller and Windows *does* have the drivers > >> for it, however it is not remapped on re-balancing. > > Does it really have a driver, i.e ivshmem specific one? > > It should have its own driver or otherwise userspace > > won't be able to access/work with it and it would be pointless > > to add such device to machine. > > No, it does not. so it's "PCI RAM controller", which is marked as NODRV in INF file, NODRV they use as a stub to prevent Windows asking for driver assuming that HW owns/manages device. And when rebalancing happens Windows completely ignores NODRV BARs which causes overlapping with devices that have PCI drivers. > > > > >> You can see on Device Manage 2 working devices with the same MMIO region - strange! > >> This may be because PCI RAM controllers can't be re-mapped? Even then, it should not be overridden. > >> Maybe we need to add a clue to the OS in ACPI regarding this range? > >> > >> 2. PCI devices with no driver installed are not re-mapped. This can be OK > >> from the Windows point of view because Resources Window does not show the MMIO range > >> for this device. > >> > >> If the other (re-mapped) device is working, is pure luck. Both Memory Regions occupy the same range > >> and have the same priority. > >> > >> We need to think about how to solve this. > >> One way would be to defer the BAR activation to the guest OS, but I am not sure of the consequences. > > deferring won't solve problem as rebalancing could happen later > > and make BARs overlap. > > Why not? If we do not activate the BAR in firmware and Windows does not have a driver > for it, will not activate it at all, right? > Why would Windows activate the device BAR if it can't use it? At least this is what I hope. > Any other idea would be appreciated. > > > > I've noticed that at startup Windows unmaps and then maps BARs > > at the same addresses where BIOS've put them before. > > Including devices without a working driver? I've just tried, it does so for ivshmem. > > > Thanks, > Marcel > > > > >> And this does not solve the ivshmem problem. > > So far the only way to avoid overlapping BARs due to Windows > > doing rebalancing for driver-less devices is to pin such > > BARs statically with _CRS in ACPI table but as Michael said > > it fragments PCI address-space. > > > >> > >> Thanks, > >> Marcel > >> > >> > >> > >> > >> > > > >