Re: [Qemu-devel] [PATCH] extend limit of physical sections number

[Peter Maydell]

On 5 November 2013 09:00, Paolo Bonzini <address@hidden> wrote:
> Il 05/11/2013 01:36, Peter Maydell ha scritto:
>> On 27 September 2013 17:49, Amos Kong <address@hidden> wrote:
>>>  # qemu -drive file=/disk0,if=none,id=v0,format=qcow2 \
>>>  -device virtio-blk-pci,drive=v0,id=v00,multifunction=on,addr=0x04.0
>>>  ....
>>>
>>> Launching guest with more than 32 virtio-blk disks,
>>> qemu will crash, because there are too many BARs.
>>>
>>> This patch brings the limit of non-tcg up by a factor
>>> of 8 (32767 / 4096), i.e. 32*8 = 256.

>> This looks really weird. Why should the memory subsystem
>> care whether we're using TCG or KVM or Xen?
>
> Because only TCG stores the section number in the low bits of the iotlb
> entry.  This is exactly what is explained in the comments.

So presumably we still crash if there are more than
32 virtio-blk disks on TCG (and indeed if more than 256
on KVM)? That doesn't seem very satisfactory...

-- PMM