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

[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?

Best Regards,
Fiona

[0]: https://forum.proxmox.com/threads/150217/
[1]: https://forum.proxmox.com/threads/149772/post-683562
[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'