----- Original Message -----
> On 2012-02-29 16:22, Amos Kong wrote:
> > ----- Original Message -----
> >> On 2012-02-29 14:30, Amos Kong wrote:
> >>> kvm_io_bus devices are used for ioevent, pit, pic, ioapic,
> >>> coalesced_mmio.
> >>>
> >>> Currently Qemu only emulates one PCI bus, it contains 32 slots,
> >>> one slot contains 8 functions, maximum of supported PCI devices:
> >>> 1 * 32 * 8 = 256. The maximum of coalesced mmio zone is 100,
> >>> each zone has an iobus devices. 300 io_bus devices is not enough.
> >>>
> >>> This patch makes the kvm_io_range array can be resized
> >>> dynamically.
> >>
> >> Is there any limit, or can userspace allocate arbitrary amounts of
> >> kernel memory this way?
> >
> > Hi Jan,
> >
> > There is a fixed array in linux-2.6/include/linux/kvm_host.h,
> > we can only register 300 devices.
> >
> > struct kvm_io_range {
> > gpa_t addr;
> > int len;
> > struct kvm_io_device *dev;
> > };
> >
> > struct kvm_io_bus {
> > int dev_count;
> > #define NR_IOBUS_DEVS 300
> > struct kvm_io_range range[NR_IOBUS_DEVS];
> > };
> > ^^^^^^^^^^^^^^
>
> Right. But doesn't your patch remove precisely this limit? So what
> limits userspace now? To register 300 million devices...?
Hi Jan,
It seems we need to reserve the limitation in kvm_host.h
#define NR_IOBUS_DEVS 600
/* Currently Qemu only emulates one PCI bus, it contains 32 slots,
one slot contains 8 functions. Only 29 slots can be used to
add multiple function devices. Maximum of supported PCI devices:
29 * 8 = 232. Each virtio-blk device needs 1 iobus device,
each virtio-net(vhost) device requires 2 such devices to service
notifications (ioevent) from rx/tx queues.
The maximum of coalesced mmio zone is 100, each zone has an iobus
devices. ioevent, pit, ioapic take less iobus devices.
So we can set max limitation to 600. */
----- check limit when register dev ----
virt/kvm/kvm_main.c:
/* Caller must hold slots_lock. */
int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
int len, struct kvm_io_device *dev)
{
struct kvm_io_bus *new_bus, *bus;
bus = kvm->buses[bus_idx];
if (bus->dev_count > NR_IOBUS_DEVS - 1) // can only register 600 devices
return -ENOSPC;
Amos.
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