Re: [PATCH v7 04/14] mm/shmem: Support memfile_notifier

[Gupta, Pankaj]

> > > +#ifdef CONFIG_MIGRATION
> > > +static int shmem_migrate_page(struct address_space *mapping,
> > > +                             struct page *newpage, struct page *page,
> > > +                             enum migrate_mode mode)
> > > +{
> > > +       struct inode *inode = mapping->host;
> > > +       struct shmem_inode_info *info = SHMEM_I(inode);
> > > +
> > > +       if (info->memfile_node.flags & MEMFILE_F_UNMOVABLE)
> > > +               return -EOPNOTSUPP;
> > > +       return migrate_page(mapping, newpage, page, mode);
> >
> > Wondering how well page migrate would work for private pages
> > on shmem memfd based backend?
>
>  From high level:
>    - KVM unset MEMFILE_F_UNMOVABLE bit to indicate it capable of
>      migrating a page.
>    - Introduce new 'migrate' callback(s) to memfile_notifier_ops for KVM
>      to register.
>    - The callback is hooked to migrate_page() here.
>    - Once page migration requested, shmem calls into the 'migrate'
>      callback(s) to perform additional steps for encrypted memory (For
>      TDX we will call TDH.MEM.PAGE.RELOCATE).

Yes, that would require additional (protocol specific) handling for 
private pages. Was trying to find where "MEMFILE_F_UNMOVABLE" flag is 
set currently?

Thanks,
Pankaj