From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:57185) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aVesF-00064h-EY for qemu-devel@nongnu.org; Tue, 16 Feb 2016 07:37:00 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aVesA-00024G-DB for qemu-devel@nongnu.org; Tue, 16 Feb 2016 07:36:59 -0500 Received: from mx1.redhat.com ([209.132.183.28]:45216) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aVesA-00023u-2L for qemu-devel@nongnu.org; Tue, 16 Feb 2016 07:36:54 -0500 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> From: Marcel Apfelbaum Message-ID: <56C317E1.1020602@redhat.com> Date: Tue, 16 Feb 2016 14:36:49 +0200 MIME-Version: 1.0 In-Reply-To: <20160216131737.7df40a1d@nial.brq.redhat.com> Content-Type: text/plain; charset=windows-1252; format=flowed 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: Igor Mammedov Cc: Xiao Guangrong , ehabkost@redhat.com, "Michael S. Tsirkin" , ghammer@redhat.com, Marcel Apfelbaum , qemu-devel@nongnu.org, lcapitulino@redhat.com, lersek@redhat.com 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. > >> 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? 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 >> >> >> >> >> >