Re: [PATCH v9 1/8] mm: Introduce memfd_restricted system call to create restricted user memory

Chao Peng
2022-11-29T14:05:59Z

On Tue, Nov 29, 2022 at 12:39:06PM +0100, David Hildenbrand wrote:
> On 29.11.22 12:21, Kirill A. Shutemov wrote:
> > On Mon, Nov 28, 2022 at 06:06:32PM -0600, Michael Roth wrote:
> > > On Tue, Oct 25, 2022 at 11:13:37PM +0800, Chao Peng wrote:
> > > > From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
> > > >
> > >
> > > <snip>
> > >
> > > > +static struct file *restrictedmem_file_create(struct file *memfd)
> > > > +{
> > > > + struct restrictedmem_data *data;
> > > > + struct address_space *mapping;
> > > > + struct inode *inode;
> > > > + struct file *file;
> > > > +
> > > > + data = kzalloc(sizeof(*data), GFP_KERNEL);
> > > > + if (!data)
> > > > + return ERR_PTR(-ENOMEM);
> > > > +
> > > > + data->memfd = memfd;
> > > > + mutex_init(&data->lock);
> > > > + INIT_LIST_HEAD(&data->notifiers);
> > > > +
> > > > + inode = alloc_anon_inode(restrictedmem_mnt->mnt_sb);
> > > > + if (IS_ERR(inode)) {
> > > > + kfree(data);
> > > > + return ERR_CAST(inode);
> > > > + }
> > > > +
> > > > + inode->i_mode |= S_IFREG;
> > > > + inode->i_op = &restrictedmem_iops;
> > > > + inode->i_mapping->private_data = data;
> > > > +
> > > > + file = alloc_file_pseudo(inode, restrictedmem_mnt,
> > > > + "restrictedmem", O_RDWR,
> > > > + &restrictedmem_fops);
> > > > + if (IS_ERR(file)) {
> > > > + iput(inode);
> > > > + kfree(data);
> > > > + return ERR_CAST(file);
> > > > + }
> > > > +
> > > > + file->f_flags |= O_LARGEFILE;
> > > > +
> > > > + mapping = memfd->f_mapping;
> > > > + mapping_set_unevictable(mapping);
> > > > + mapping_set_gfp_mask(mapping,
> > > > + mapping_gfp_mask(mapping) & ~__GFP_MOVABLE);
> > >
> > > Is this supposed to prevent migration of pages being used for
> > > restrictedmem/shmem backend?
> >
> > Yes, my bad. I expected it to prevent migration, but it is not true.
>
> Maybe add a comment that these pages are not movable and we don't want to
> place them into movable pageblocks (including CMA and ZONE_MOVABLE). That's
> the primary purpose of the GFP mask here.

Yes I can do that.

Chao
>
> --
> Thanks,
>
> David / dhildenb