Am 12.07.24 um 15:26 schrieb Igor Mammedov:
> On Fri, 12 Jul 2024 14:24:40 +0200
> Fiona Ebner <f.eb...@proxmox.com> wrote:
>
>> Hi,
>>
>> Am 21.06.24 um 14:05 schrieb Gerd Hoffmann:
>>> On Wed, Jun 19, 2024 at 11:21:14AM GMT, John Levon wrote:
>>>> Older 32-bit Linux VMs (including Ubuntu 16.10) have issues with the
>>>> 64-bit pci io window, failing during boot with errors like:
>>>
>>> Well. Why people would use *that* ubuntu version is not clear to me.
>>> It's *loooooong* out of support. Even the LTS version from that year
>>> (16.04) is not supported any more. But it is at least available for
>>> download still, so I gave it a spin.
>>>
>>> Turns out it apparently can't deal with PCI bars mapped above 16TB (aka
>>> 44 phys-bits). Test patch below.
>>>
>>> take care,
>>> Gerd
>>>
>>> diff --git a/src/fw/pciinit.c b/src/fw/pciinit.c
>>> index bb44dc296047..a43876a931c9 100644
>>> --- a/src/fw/pciinit.c
>>> +++ b/src/fw/pciinit.c
>>> @@ -1189,11 +1189,16 @@ pci_setup(void)
>>>
>>> if (CPUPhysBits) {
>>> pci_mem64_top = 1LL << CPUPhysBits;
>>> - if (CPUPhysBits > 46) {
>>> - // Old linux kernels have trouble dealing with more than 46
>>> - // phys-bits, so avoid that for now. Seems to be a bug in the
>>> - // virtio-pci driver. Reported: centos-7, ubuntu-18.04
>>> - pci_mem64_top = 1LL << 46;
>>> + if (CPUPhysBits > 44) {
>>> + // Old linux kernels have trouble dealing with more than 44/46
>>> + // phys-bits. Seems to be a bug in the virtio-pci driver.
>>> + // 46: centos-7, ubuntu-18.04
>>> + // 44: ubuntu-16.04
>>> + // Limit the used address space to mitigate the bug, except we
>>> are
>>> + // running in a guest with more than 1TB of memory installed.
>>> + if (RamSizeOver4G < (1LL << 40)) {
>>> + pci_mem64_top = 1LL << 44;
>>> + }
>>> }
>>> }
>>>
>>
>> we've also had two reports about issues with 32-bit guests now[0][1]
>> (both had '-m 4096' in the QEMU commandline), which I was able to
>> reproduce with a 32-bit Debian 12.6 install, so nothing ancient ;) The
>> QEMU commandline is below[2].
>
> is it also reproducible with upstream kernel?
> if yes, it would be better to fix that on guest kernel side,
> rather than in SeaBIOS which has no idea what guest OS is going to be
> running after it.
>
Turns out it's only kernels with PAE. The 6.1 Debian kernel without PAE
boots fine (but the PAE was the one installed by default). I built a
6.10 kernel and it also boots fine, a 6.10 build with PAE doesn't.
>> Unfortunately, it still fails to boot, even with the "limit address
>> space used for pci devices, part two" patch applied on top of rel-1.16.3
>> (and using current QEMU master).
>>
>> It boots fine with '-m 3583', but not anymore with '-m 3584'. So is
>> bumping the limit for the check necessary after all?
>>
>> Best Regards,
>> Fiona
>>
>> [0]: https://forum.proxmox.com/threads/150217/
>
>> [1]: https://forum.proxmox.com/threads/149772/post-683562
> well, with current QEMU master branch (I assume it haven't even got topic
> patch yet)
> ./qemu-system-x86_64 --enable-kvm -cpu host -smp 4 -snapshot -m 4096 -M
> pc-i440fx-6.1 winxp_x86_build2600
> following CLI boots just fine an 32-bit XP on Haswell host.
>
> Also using 'host' with ancient OS, is basically asking for trouble.
> If it works for user with old 'XP contemporary' CPU model, user should use
> that
> instead or workarounds (aka it's management task to configure CLI in
> compatible with OS manner).
>
> From suspicions config options in that post I see 'viommu' and 'vmgenid',
> are you sure XP even knows what to do with that, perhaps it triggers BSOD.
>
No idea why the user enabled viommu for XP. vmgenid is added by our
management stack by default and I don't remember it having ever caused
problems. The user said the VM booted fine after adding lm=off to the
CPU options. I'm not super interested in the Windows case to be honest O:)
>> [2]:
>>
>>> ./qemu-system-x86_64 \
>>> -accel 'kvm' \
>>> -cpu 'host' \
>>> -chardev
>>> 'socket,id=qmp,path=/var/run/qemu-server/121.qmp,server=on,wait=off' \
>>> -mon 'chardev=qmp,mode=control' \
>>> -chardev 'socket,id=qmp-event,path=/var/run/qmeventd.sock,reconnect=5' \
>>> -mon 'chardev=qmp-event,mode=control' \
>>> -pidfile /var/run/qemu-server/121.pid \
>>> -smp '4,sockets=1,cores=4,maxcpus=4' \
>>> -nodefaults \
>>> -vnc 'unix:/var/run/qemu-server/121.vnc,password=on' \
>>> -m 4096 \
>>> -device 'pci-bridge,id=pci.3,chassis_nr=3,bus=pci.0,addr=0x5' \
>>> -device 'VGA,id=vga,bus=pci.0,addr=0x2' \
>>> -device 'virtio-scsi-pci,id=virtioscsi0,bus=pci.3,addr=0x1' \
>>> -drive
>>> 'file=/dev/lvmthinbig/vm-121-disk-0,if=none,id=drive-scsi0,format=raw,cache=none,aio=io_uring,detect-zeroes=on'
>>> \
>>> -device
>>> 'scsi-hd,bus=virtioscsi0.0,channel=0,scsi-id=0,lun=0,drive=drive-scsi0,id=scsi0,bootindex=100'
>>> \
>>> -machine 'type=pc'
>
> can you try to boot with q35 + intel iommu enabled
> and/or force virtio into legacy mode.
>
I tried
> -device 'intel-iommu' \
> -machine 'type=q35'
and intel_iommu=on in the guest's kernel cmdline, but it still failed
with kernels with PAE.
Appending 'disable-modern=on,disable-legacy=off' to the virtio-scsi-pci
line made it work however (also with pc machine) :)
Best Regards,
Fiona
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