[SeaBIOS] Re: [PATCH v2 4/4] only enable 64bit pci io window when RAM >64G

[Fiona Ebner]

Am 12.07.24 um 14:24 schrieb Fiona Ebner:
> 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].
>
> 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?

Sorry for bumping this again, but we got a new report about OpenBSD 7.6
being affected too (see [3] and the following posts in the forum
thread). In particular, the user reports a regression with PCIe
passthrough failing and seeing "mem address conflict" messages in dmesg.
I could reproduce the latter using [4], i.e. seeing the messages and
checked that it is caused by 96a8d130 ("be less conservative with the
64bit pci io window"). The user reported that using 2 GiB of RAM makes
the passthrough work again and the messages disappear.

The messages are still present when I test with current SeaBIOS master
2424e4c0 ("esp-scsi: indicate acceptance of MESSAGE IN phase data") and
QEMU v9.1.1.

Note that I also get the messages without the vfio-pci device, but since
I wasn't able to reproduce the passthrough failure, it is what I have to
work with.

Best Regards,
Fiona

[3]: https://forum.proxmox.com/threads/149772/post-713842
[4]: https://ftp2.eu.openbsd.org/pub/OpenBSD/7.6/amd64/install76.iso

QEMU commandline with which I observed the messages:
> ./qemu-system-x86_64 \
>   -accel kvm \
>   -pidfile /var/run/qemu-server/122.pid \
>   -chardev 'socket,id=qmp,path=/var/run/qemu-server/122.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' \
>   -smp '8,sockets=1,cores=8,maxcpus=8' \
>   -nodefaults \
>   -vnc 'unix:/var/run/qemu-server/122.vnc,password=on' \
>   -cpu host \
>   -m 4096 \
>   -device 'pci-bridge,id=pci.3,chassis_nr=3,bus=pci.0,addr=0x5' \
>   -device 'vfio-pci,host=0000:00:1b.0,id=hostpci0,bus=pci.0,addr=0x10' \
>   -device 'VGA,id=vga,bus=pci.0,addr=0x2' \
>   -device 'virtio-scsi-pci,id=virtioscsi0,bus=pci.3,addr=0x1' \
>   -drive 'file=/dev/zvol/zfs/vm-122-disk-0,if=none,id=drive-scsi0,format=raw' \
>   -device 'scsi-hd,bus=virtioscsi0.0,channel=0,scsi-id=0,lun=0,drive=drive-scsi0,id=scsi0,bootindex=100' \
>   -machine 'type=pc'
> [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'
>
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