Re: [PATCH v1 0/3] migration: Fixes to the 'background-snapshot' code

[Andrey Gruzdev]

On 24.03.2021 01:21, Peter Xu wrote:

> On Fri, Mar 19, 2021 at 05:52:46PM +0300, Andrey Gruzdev wrote:
> > Changes v0->v1:
> >  * Using qemu_real_host_page_size instead of TARGET_PAGE_SIZE for host
> >    page size in ram_block_populate_pages()
> >  * More elegant implementation of ram_block_populate_pages()
> >
> > This patch series contains:
> >  * Fix to the issue with occasionally truncated non-iterable device state
> >  * Solution to compatibility issues with virtio-balloon device
> >  * Fix to the issue when discarded or never populated pages miss UFFD
> >    write protection and get into migration stream in dirty state
> >
> > Andrey Gruzdev (3):
> >   migration: Fix missing qemu_fflush() on buffer file in
> >     bg_migration_thread
> >   migration: Inhibit virtio-balloon for the duration of background
> >     snapshot
> >   migration: Pre-fault memory before starting background snasphot
> >       
> Unless Andrey would like to respin a new version, this version looks good to me
> (I don't think the adding new helper issue in patch 1 is a blocker):
>
> Reviewed-by: Peter Xu <peterx@redhat.com>
>     
Thanks.
> I'm also looking into introducing UFFD_FEATURE_WP_UNALLOCATED so as to
> wr-protect page holes too for a uffd-wp region when the feature bit is set.
> With that feature we should be able to avoid pre-fault as what we do in the
> last patch of this series.  However even if that can work out, we'll still need
> this for old kernel anyways.
>     
I'm curious this new feature is based on adding wr-protection at the level of VMAs,
so we won't miss write faults for missing pages?
> Thanks,
>
>