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

Gupta, Pankaj
2022-07-14T04:15:51Z

>>>>> +#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?
>
> It's set with memfile_register_notifier() in patch 13.

o.k.

Thanks,

Pankaj