Re: [PATCH v2 5/6] virtio-mem: use page_offline_(start|end) when setting PageOffline()

From: Oscar Salvador
Date: Tue May 25 2021 - 04:20:51 EST

On Fri, May 14, 2021 at 07:22:46PM +0200, David Hildenbrand wrote:
> Let's properly use page_offline_(start|end) to synchronize setting
> PageOffline(), so we won't have valid page access to unplugged memory
> regions from /proc/kcore.
> Existing balloon implementations usually allow reading inflated memory;
> doing so might result in unnecessary overhead in the hypervisor, which
> is currently the case with virtio-mem.
> For future virtio-mem use cases, it will be different when using shmem,
> huge pages, !anonymous private mappings, ... as backing storage for a VM.
> virtio-mem unplugged memory must no longer be accessed and access might
> result in undefined behavior. There will be a virtio spec extension to
> document this change, including a new feature flag indicating the
> changed behavior. We really don't want to race against PFN walkers
> reading random page content.
> Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>

Reviewed-by: Oscar Salvador <osalvador@xxxxxxx>

Oscar Salvador