Re: [virtio-dev] [PATCH v3 00/15] virtio-mem: paravirtualized memory

David Hildenbrand
2020-05-14T11:48:02Z

On 14.05.20 13:10, David Hildenbrand wrote:
> On 14.05.20 12:12, David Hildenbrand wrote:
>> On 14.05.20 12:02, teawater wrote:
>>>
>>>
>>>> 2020年5月14日 16:48，David Hildenbrand <david@redhat.com> 写道：
>>>>
>>>> On 14.05.20 08:44, teawater wrote:
>>>>> Hi David,
>>>>>
>>>>> I got a kernel warning with v2 and v3.
>>>>
>>>> Hi Hui,
>>>>
>>>> thanks for playing with the latest versions. Surprisingly, I can
>>>> reproduce even by hotplugging a DIMM instead as well - that's good, so
>>>> it's not related to virtio-mem, lol. Seems to be some QEMU setup issue
>>>> with older machine types.
>>>>
>>>> Can you switch to a newer qemu machine version, especially
>>>> pc-i440fx-5.0? Both, hotplugging DIMMs and virtio-mem works for me with
>>>> that QEMU machine just fine.
>>>
>>> I still could reproduce this issue with pc-i440fx-5.0 or pc. Did I miss anything?
>>>
>>
>> Below I don't even see virtio_mem. I had to repair the image (filesystem
>> fsck) because it was broken, can you try that as well?
>>
>> Also, it would be great if you could test with v4.
>>
>
> Correction, something seems to be broken either in QEMU or the kernel. Once I
> define a DIMM so it's added and online during boot, I get these issues:
>
> (I have virtio-mem v4 installed in the guest)
>
> #! /bin/bash
> sudo x86_64-softmmu/qemu-system-x86_64 \
> -machine pc-i440fx-5.0,accel=kvm,usb=off \
> -cpu host \
> -no-reboot \
> -nographic \
> -device ide-hd,drive=hd \
> -drive if=none,id=hd,file=/home/dhildenb/git/Fedora-Cloud-Base-31-1.9.x86_64.qcow2,format=qcow2 \
> -m 1g,slots=10,maxmem=2G \
> -smp 1 \
> -object memory-backend-ram,id=mem0,size=256m \
> -device pc-dimm,id=dimm0,memdev=mem0 \
> -s \
> -monitor unix:/var/tmp/monitor,server,nowait
>
>
> Without the DIMM it seems to work just fine.
>

And another correction.

Using QEMU v5.0.0, Linux 5.7-rc5, untouched
Fedora-Cloud-Base-32-1.6.x86_64.qcow2, I get even without any memory hotplug:

#! /bin/bash
sudo x86_64-softmmu/qemu-system-x86_64 \
-machine pc-i440fx-5.0,accel=kvm,usb=off \
-cpu host \
-no-reboot \
-nographic \
-device ide-hd,drive=hd \
-drive if=none,id=hd,file=/home/dhildenb/git/Fedora-Cloud-Base-32-1.6.x86_64.qcow2,format=qcow2 \
-m 5g,slots=10,maxmem=6G \
-smp 1 \
-s \
-kernel /home/dhildenb/git/linux/arch/x86/boot/bzImage \
-append "console=ttyS0 rd.shell nokaslr swiotlb=noforce" \
-monitor unix:/var/tmp/monitor,server,nowait

Observe how big the initial RAM even is!

So this is no DIMM/hotplug/virtio_mem issue. With memory hotplug, it seems to get
more likely to trigger if "swiotlb=noforce" is not specified.

"swiotlb=noforce" seems to trigger some pre-existing issue here. Without
"swiotlb=noforce", I was only able to observe this via pc-i440fx-2.1,

--
Thanks,

David / dhildenb