On Thu, Dec 01, 2022 at 06:16:46PM -0800, Vishal Annapurve wrote:

On Tue, Oct 25, 2022 at 8:18 AM Chao Peng [off-list ref] wrote:

quoted

...

quoted

+}
+
+SYSCALL_DEFINE1(memfd_restricted, unsigned int, flags)
+{

Looking at the underlying shmem implementation, there seems to be no
way to enable transparent huge pages specifically for restricted memfd
files.

Michael discussed earlier about tweaking
/sys/kernel/mm/transparent_hugepage/shmem_enabled setting to allow
hugepages to be used while backing restricted memfd. Such a change
will affect the rest of the shmem usecases as well. Even setting the
shmem_enabled policy to "advise" wouldn't help unless file based
advise for hugepage allocation is implemented.

Had a look at fadvise() and looks it does not support HUGEPAGE for any
filesystem yet.

Does it make sense to provide a flag here to allow creating restricted
memfds backed possibly by huge pages to give a more granular control?

We do have a unused 'flags' can be extended for such usage, but I would
let Kirill have further look, perhaps need more discussions.

Chao

quoted

+       struct file *file, *restricted_file;
+       int fd, err;
+
+       if (flags)
+               return -EINVAL;
+
+       fd = get_unused_fd_flags(0);
+       if (fd < 0)
+               return fd;
+
+       file = shmem_file_setup("memfd:restrictedmem", 0, VM_NORESERVE);
+       if (IS_ERR(file)) {
+               err = PTR_ERR(file);
+               goto err_fd;
+       }
+       file->f_mode |= FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE;
+       file->f_flags |= O_LARGEFILE;
+
+       restricted_file = restrictedmem_file_create(file);
+       if (IS_ERR(restricted_file)) {
+               err = PTR_ERR(restricted_file);
+               fput(file);
+               goto err_fd;
+       }
+
+       fd_install(fd, restricted_file);
+       return fd;
+err_fd:
+       put_unused_fd(fd);
+       return err;
+}
+
+void restrictedmem_register_notifier(struct file *file,
+                                    struct restrictedmem_notifier *notifier)
+{
+       struct restrictedmem_data *data = file->f_mapping->private_data;
+
+       mutex_lock(&data->lock);
+       list_add(&notifier->list, &data->notifiers);
+       mutex_unlock(&data->lock);
+}
+EXPORT_SYMBOL_GPL(restrictedmem_register_notifier);
+
+void restrictedmem_unregister_notifier(struct file *file,
+                                      struct restrictedmem_notifier *notifier)
+{
+       struct restrictedmem_data *data = file->f_mapping->private_data;
+
+       mutex_lock(&data->lock);
+       list_del(&notifier->list);
+       mutex_unlock(&data->lock);
+}
+EXPORT_SYMBOL_GPL(restrictedmem_unregister_notifier);
+
+int restrictedmem_get_page(struct file *file, pgoff_t offset,
+                          struct page **pagep, int *order)
+{
+       struct restrictedmem_data *data = file->f_mapping->private_data;
+       struct file *memfd = data->memfd;
+       struct page *page;
+       int ret;
+
+       ret = shmem_getpage(file_inode(memfd), offset, &page, SGP_WRITE);
+       if (ret)
+               return ret;
+
+       *pagep = page;
+       if (order)
+               *order = thp_order(compound_head(page));
+
+       SetPageUptodate(page);
+       unlock_page(page);
+
+       return 0;
+}
+EXPORT_SYMBOL_GPL(restrictedmem_get_page);
--
2.25.1