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

Gupta, Pankaj
2022-07-13T10:01:40Z

>>> +#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