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

[David Hildenbrand]

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