Re: [Qemu-discuss] PCI device limit?

[Scott Sullivan]

On 03/18/2014 10:07 AM, Scott Sullivan wrote:
> Hello,
>
> I am using QEMU 1.7.0. With this version, I am able to add up to 32 
> PCI devices. If I attempt to add anything more, my VMs QEMU process 
> shuts itself down shortly after I select the kernel to boot in Grub.
>
> Per this page:
>
> http://wiki.qemu.org/Features/PCIBridgeHotplug#Roadmap
>
> It sounds like I need to start QEMU with "-M 1.6" ? However that 
> appears to be an invalid option to qemu-system-x86_64. What's curious, 
> is that on old QEMU-KVM, I am able to add all the way up to 52 PCI 
> devices (virtio disks) without any issues. Is there something I need 
> to do on QEMU to enable the PCI bridge? In the test scenario, the 
> arguments given to QEMU and QEMU-KVM were the same.

So after more investigation, when I have more than 32 PCI devices, it 
does create extra PCI bridges I see from the qemu command line:

 -device pci-bridge,chassis_nr=1

However, once it starts to load the linux kernel after selecting it from 
grub, qemu aborts with this:

qemu-system-x86_64: 
/home/rpmbuild/packages/rpmbuild/BUILD/qemu/exec.c:756: 
phys_section_add: Assertion `next_map.sections_nb < (1 << 12)' failed.

It appears my issue here is the same one as this:

http://permalink.gmane.org/gmane.comp.emulators.qemu/234307

It doesn't look like the pci bridge functionality works properly. In the 
old qemu-kvm, using the same arguments, I can boot the instance and see 
all the way up to 104 pci devices (as high as i've tested) with 3 PCI 
bridges created.