Re: [PATCH] virtio-mem: Fix the bitmap index of the section offset

[David Hildenbrand <david@redhat.com>]

On 19.12.22 02:21, Chenyi Qiang wrote:
> 
> 
> On 12/16/2022 6:30 PM, David Hildenbrand wrote:
>> On 16.12.22 09:52, David Hildenbrand wrote:
>>> On 16.12.22 07:22, Chenyi Qiang wrote:
>>>> vmem->bitmap indexes the memory region of the virtio-mem backend at a
>>>> granularity of block_size. To calculate the index of target section
>>>> offset,
>>>> the block_size should be divided instead of the bitmap_size.
>>>
>>> I'm curious, what's the user-visible effect and how did you identify
>>> this issue?
>>>
>>> IIUC, we could end up our search for a plugged/unplugged block "too
>>> late", such that we miss to process blocks.
>>>
>>> That would be the case if the bitmap_size < block_size, which should
>>> effectively always happen ...
>>>
>>>
>>> unplug_all and migration would be affected, which is why a simple test
>>> case without a guest reboot/migration wouldn't run into it.
>>
>> I just realized that unplug_all is fine because only vfio implements the
>> ram_discard_listener so far and always sets
>> double_discard_supported=true. So migration should be the issue (and
>> IIRC migration with VFIO is still shaky).
> 
> Yes, actually, no obvious visible effect on my side. I was just learning
> the RamDiscardManager interface and found this issue. :)

Good, thanks.

Queuing this to

https://github.com/davidhildenbrand/qemu.git mem-next

-- 
Thanks,

David / dhildenb