Re: [PATCH 1/2] KVM: arm64: Fix spurious warning for benign stage 2 teardown race

["Lorenzo Stoakes (ARM)" <ljs@kernel.org>]

On Mon, Aug 17, 2026 at 08:38:37AM +0800, Yao Yuan wrote:
> On Fri, Aug 14, 2026 at 09:48:39AM +0800, Lorenzo Stoakes (ARM) wrote:
> > OK so - I confused myself here :)
> >
> > The underlying issue here is that I am working back from a situation where
> > I can't quite recall what I did, but am rather reconstructing it based on
> > what was observed.
> >
> > And you're right - this stack makes no sense for an L2 VM being torn down,
> > rather only the L0 being torn down.
> >
> > So clearly this is what I did, and the correction should be to say this at
> > the start of the commit message.
>
> Ah I see.  I agree the race is there. Below is just an idea
> in my mind for reproducing this, hope this is helpful to you :-)
>
> migratepages (https://man7.org/linux/man-pages/man8/migratepages.8.html) can
> help to trigger the MMU notifier to qemu/kvmtool easily on 2P system, meanwhile
> kill the qemu/kvmtool on L0 to reprouduce the racing. For 1P system kernel has
> numa=fake parameter to generate more NUMAs there.
>

Ah nice thanks! There's also /proc/sys/vm/compact_memory so you can do:

$ echo 1 | sudo tee /proc/sys/vm/compact_memory

To trigger immediate memory compaction (and thus migration) also :)

--
Cheers, Lorenzo