Re: [PATCH v3] KVM: Resize kvm_io_range array dynamically

[Jan Kiszka <jan.kiszka@siemens.com>]

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...?

Jan

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