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Re: [Qemu-devel] [PATCH] extend limit of physical sections number
From: |
Peter Maydell |
Subject: |
Re: [Qemu-devel] [PATCH] extend limit of physical sections number |
Date: |
Tue, 5 Nov 2013 12:23:43 +0000 |
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