On Wed, Feb 13, 2013 at 11:34:52AM +0100, Jan Kiszka wrote: > On 2013-02-13 11:24, Michael S. Tsirkin wrote: > > On Wed, Feb 13, 2013 at 06:06:37PM +1300, Alexey Korolev wrote: > >> Sometime ago I reported an issue about guest OS hang when 64bit BAR > >> present. > >> http://lists.gnu.org/archive/html/qemu-devel/2012-01/msg03189.html > >> http://lists.gnu.org/archive/html/qemu-devel/2012-12/msg00413.html > >> > >> Some more investigation has been done, so in this post I'll try to explain > >> why it happens and offer possible solutions: > >> > >> *When the issue happens* > >> The issue occurs on Linux guest OS if kernel version <2.6.36 > >> A Guest OS hangs on boot when a 64bit PCI BAR is present in a system (if > >> we use ivshmem driver for example) and occupies range within first > >> 4 GB. > >> > >> *How to reproduce* > >> I used the following qemu command to reproduce the case: > >> /usr/local/bin/qemu-system-x86_64 -M pc-1.3 -enable-kvm -m 2000 -smp > >> 1,sockets=1,cores=1,threads=1 -name Rh5332 -chardev > >> socket,id=charmonitor,path=/var/lib/libvirt/qemu/Rh5332.monitor,server,nowait > >> -mon chardev=charmonitor,id=monitor,mode=readline -rtc > >> base=utc -boot cd -drive > >> file=/home/akorolev/rh5332.img,if=none,id=drive-ide0-0-0,format=raw -device > >> ide-drive,bus=ide.0,unit=0,drive=drive-ide0-0-0,id=ide0-0-0 -chardev > >> file,id=charserial0,path=/home/akorolev/serial.log -device > >> isa-serial,chardev=charserial0,id=serial0 -usb -vnc 127.0.0.1:0 -k en-us > >> -vga cirrus -device ivshmem,shm,size=32M-device > >> virtio-balloon-pci,id=balloon0 > >> > >> Tried different guests: Centos 5.8 64bit, RHEL 5.3 32bit, FC 12 64bit on > >> all machines hang occurs in 100% cases > >> > >> *Why it happens* > >> The issue basically comes from Linux PCI enumeration code. > >> > >> The OS enumerates 64BIT bars when device is enabled using the following > >> procedure. > >> 1. Write all FF's to lower half of 64bit BAR > >> 2. Write address back to lower half of 64bit BAR > >> 3. Write all FF's to higher half of 64bit BAR > >> 4. Write address back to higher half of 64bit BAR > >> > >> For qemu it means that qemu pci_default_write_config() recevies all FFs > >> for lower part of the 64bit BAR. > >> Then it applies the mask and converts the value to "All FF's - size + 1" > >> (FE000000 if size is 32MB). > >> > >> So for short period of time the range [0xFE000000 - 0xFFFFFFFF] will be > >> occupied by ivshmem resource. > >> For some reason it is lethal for further boot process. > >> > >> We have found that boot process screws up completely if kvm-apic-msi range > >> is overlapped even for short period of time. (We still don't > >> know why it happens, hope that the qemu maintainers can answer?) > >> > >> If we look at kvm-apic-msi memory region it is a non-overlapable memory > >> region with hardcoded address range [0xFEE00000 - 0xFEF00000]. > > > > Thanks for looking into this! > > > >> Here is a log we collected from render_memory_regions: > >> > >> system overlap 0 pri 0 [0x0 - 0x7fffffffffffffff] > >> kvmvapic-rom overlap 1 pri 1000 [0xca000 - 0xcd000] > >> pc.ram overlap 0 pri 0 [0xca000 - 0xcd000] > >> ++ pc.ram [0xca000 - 0xcd000] is added to view > >> .................... > >> smram-region overlap 1 pri 1 [0xa0000 - 0xc0000] > >> pci overlap 0 pri 0 [0xa0000 - 0xc0000] > >> cirrus-lowmem-container overlap 1 pri 1 [0xa0000 - 0xc0000] > >> cirrus-low-memory overlap 0 pri 0 [0xa0000 - 0xc0000] > >> ++cirrus-low-memory [0xa0000 - 0xc0000] is added to view > >> kvm-ioapic overlap 0 pri 0 [0xfec00000 - 0xfec01000] > >> ++kvm-ioapic [0xfec00000 - 0xfec01000] is added to view > >> pci-hole64 overlap 0 pri 0 [0x100000000 - 0x4000000100000000] > >> pci overlap 0 pri 0 [0x100000000 - 0x4000000100000000] > >> pci-hole overlap 0 pri 0 [0x7d000000 - 0x100000000] > > > > So we have ioapic and pci-hole which should be non-overlap, > > actually overlap each other. > > Isn't this a problem? > > > >> pci overlap 0 pri 0 [0x7d000000 - 0x100000000] > >> ivshmem-bar2-container overlap 1 pri 1 [0xfe000000 - > >> 0x100000000] > >> ivshmem.bar2 overlap 0 pri 0 [0xfe000000 - 0x100000000] > >> ++ivshmem.bar2 [0xfe000000 - 0xfec00000] is added to view > >> ++ivshmem.bar2 [0xfec01000 - 0x100000000] is added to view > >> ivshmem-mmio overlap 1 pri 1 [0xfebf1000 - 0xfebf1100] > >> e1000-mmio overlap 1 pri 1 [0xfeba0000 - 0xfebc0000] > >> cirrus-mmio overlap 1 pri 1 [0xfebf0000 - 0xfebf1000] > >> cirrus-pci-bar0 overlap 1 pri 1 [0xfa000000 - 0xfc000000] > >> vga.vram overlap 1 pri 1 [0xfa000000 - 0xfa800000] > >> ++vga.vram [0xfa000000 - 0xfa800000] is added to view > >> cirrus-bitblt-mmio overlap 0 pri 0 [0xfb000000 - > >> 0xfb400000] > >> ++cirrus-bitblt-mmio [0xfb000000 - 0xfb400000] is added to > >> view > >> cirrus-linear-io overlap 0 pri 0 [0xfa000000 - 0xfa800000] > >> pc.bios overlap 0 pri 0 [0xfffe0000 - 0x100000000] > >> ram-below-4g overlap 0 pri 0 [0x0 - 0x7d000000] > >> pc.ram overlap 0 pri 0 [0x0 - 0x7d000000] > >> ++pc.ram [0x0 - 0xa0000] is added to view > >> ++pc.ram [0x100000 - 0x7d000000] is added to view > >> kvm-apic-msi overlap 0 pri 0 [0xfee00000 - 0xfef00000] > >> > >> As you can see from log the kvm-apic-msi is enumarated last when range > >> [0xfee00000 - 0xfef00000] is already occupied by ivshmem.bar2 > >> [0xfec01000 - 0x100000000]. > >> > >> > >> *Possible solutions* > >> Solution 1. Probably the best would be adding the rule that regions which > >> may not be overlapped are added to view first (In in other words > >> regions which must not be overlapped have the highest priority). Please > >> find patch in the following message. > >> > >> Solution 2. Raise priority of kvm-apic-msi resource. This is a bit > >> misleading solution, as priority is only applicable for overlap-able > >> regions, but this region must not be overlapped. > >> > >> Solution 3. Fix the issue at PCI level. Track if the resource is 64bit and > >> apply changes if both parts of 64bit BAR are programmed. (It > >> appears that real PCI bus controllers are smart enough to track 64bit BAR > >> writes on PC, so qemu could do the same? Drawbacks are that > >> tracking PCI writes is bit cumbersome, and such tracking may appear to > >> somebody as a hack) > >> > >> > >> Alexey > > > > I have to say I don't understand what does the overlap attribute > > supposed to do, exactly. > > > > In practice it currently seems to be ignored. > > > > How about we drop it and rely exclusively on priorities? > > Isn't it a guest bug if it maps a PCI resource over the APIC window? How > should the guest access that region then? With in-kernel APIC, it will > remain unaccessible, even if you raise the prio of that PCI region over > the APIC as the kernel will prioritize the latter.
Yes that would be fine (it's a temporary condition while sizing the BARs). The problem, I think, is that currently apic has default priority (0) so PCI regions can mask it during sizing. > > It's probably easier to just give the apic high priority. > > there's precedent - kvmvapic does: > > > > memory_region_add_subregion_overlap(as, rom_paddr, &s->rom, 1000); > > > > Jan, could you please clarify where did the value 1000 come from? > > To ensure that the VAPIC region is always accessible. > > > > > Maybe we need some predefined priority values in memory.h > > > > That makes some sense, sure. > > Jan > > -- > Siemens AG, Corporate Technology, CT RTC ITP SDP-DE > Corporate Competence Center Embedded Linux
