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

Gupta, Pankaj
2022-07-12T18:03:06Z

On 7/6/2022 10:20 AM, Chao Peng wrote:
> From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
>
> Implement shmem as a memfile_notifier backing store. Essentially it
> interacts with the memfile_notifier feature flags for userspace
> access/page migration/page reclaiming and implements the necessary
> memfile_backing_store callbacks.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> ---
> include/linux/shmem_fs.h | 2 +
> mm/shmem.c | 109 ++++++++++++++++++++++++++++++++++++++-
> 2 files changed, 110 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
> index a68f982f22d1..6031c0b08d26 100644
> --- a/include/linux/shmem_fs.h
> +++ b/include/linux/shmem_fs.h
> @@ -9,6 +9,7 @@
> #include <linux/percpu_counter.h>
> #include <linux/xattr.h>
> #include <linux/fs_parser.h>
> +#include <linux/memfile_notifier.h>
>
> /* inode in-kernel data */
>
> @@ -25,6 +26,7 @@ struct shmem_inode_info {
> struct simple_xattrs xattrs; /* list of xattrs */
> atomic_t stop_eviction; /* hold when working on inode */
> struct timespec64 i_crtime; /* file creation time */
> + struct memfile_node memfile_node; /* memfile node */
> struct inode vfs_inode;
> };
>
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 6c8aef15a17d..627e315c3b4d 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -905,6 +905,17 @@ static struct folio *shmem_get_partial_folio(struct inode *inode, pgoff_t index)
> return page ? page_folio(page) : NULL;
> }
>
> +static void notify_invalidate(struct inode *inode, struct folio *folio,
> + pgoff_t start, pgoff_t end)
> +{
> + struct shmem_inode_info *info = SHMEM_I(inode);
> +
> + start = max(start, folio->index);
> + end = min(end, folio->index + folio_nr_pages(folio));
> +
> + memfile_notifier_invalidate(&info->memfile_node, start, end);
> +}
> +
> /*
> * Remove range of pages and swap entries from page cache, and free them.
> * If !unfalloc, truncate or punch hole; if unfalloc, undo failed fallocate.
> @@ -948,6 +959,8 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend,
> }
> index += folio_nr_pages(folio) - 1;
>
> + notify_invalidate(inode, folio, start, end);
> +
> if (!unfalloc || !folio_test_uptodate(folio))
> truncate_inode_folio(mapping, folio);
> folio_unlock(folio);
> @@ -1021,6 +1034,9 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend,
> index--;
> break;
> }
> +
> + notify_invalidate(inode, folio, start, end);
> +
> VM_BUG_ON_FOLIO(folio_test_writeback(folio),
> folio);
> truncate_inode_folio(mapping, folio);
> @@ -1092,6 +1108,13 @@ static int shmem_setattr(struct user_namespace *mnt_userns,
> (newsize > oldsize && (info->seals & F_SEAL_GROW)))
> return -EPERM;
>
> + if (info->memfile_node.flags & MEMFILE_F_USER_INACCESSIBLE) {
> + if (oldsize)
> + return -EPERM;
> + if (!PAGE_ALIGNED(newsize))
> + return -EINVAL;
> + }
> +
> if (newsize != oldsize) {
> error = shmem_reacct_size(SHMEM_I(inode)->flags,
> oldsize, newsize);
> @@ -1336,6 +1359,8 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc)
> goto redirty;
> if (!total_swap_pages)
> goto redirty;
> + if (info->memfile_node.flags & MEMFILE_F_UNRECLAIMABLE)
> + goto redirty;
>
> /*
> * Our capabilities prevent regular writeback or sync from ever calling
> @@ -2271,6 +2296,9 @@ static int shmem_mmap(struct file *file, struct vm_area_struct *vma)
> if (ret)
> return ret;
>
> + if (info->memfile_node.flags & MEMFILE_F_USER_INACCESSIBLE)
> + return -EPERM;
> +
> /* arm64 - allow memory tagging on RAM-based files */
> vma->vm_flags |= VM_MTE_ALLOWED;
>
> @@ -2306,6 +2334,7 @@ static struct inode *shmem_get_inode(struct super_block *sb, const struct inode
> info->i_crtime = inode->i_mtime;
> INIT_LIST_HEAD(&info->shrinklist);
> INIT_LIST_HEAD(&info->swaplist);
> + memfile_node_init(&info->memfile_node);
> simple_xattrs_init(&info->xattrs);
> cache_no_acl(inode);
> mapping_set_large_folios(inode->i_mapping);
> @@ -2477,6 +2506,8 @@ shmem_write_begin(struct file *file, struct address_space *mapping,
> if ((info->seals & F_SEAL_GROW) && pos + len > inode->i_size)
> return -EPERM;
> }
> + if (unlikely(info->memfile_node.flags & MEMFILE_F_USER_INACCESSIBLE))
> + return -EPERM;
>
> if (unlikely(info->seals & F_SEAL_AUTO_ALLOCATE))
> sgp = SGP_NOALLOC;
> @@ -2556,6 +2587,13 @@ static ssize_t shmem_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
> end_index = i_size >> PAGE_SHIFT;
> if (index > end_index)
> break;
> +
> + if (SHMEM_I(inode)->memfile_node.flags &
> + MEMFILE_F_USER_INACCESSIBLE) {
> + error = -EPERM;
> + break;
> + }
> +
> if (index == end_index) {
> nr = i_size & ~PAGE_MASK;
> if (nr <= offset)
> @@ -2697,6 +2735,12 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset,
> goto out;
> }
>
> + if ((info->memfile_node.flags & MEMFILE_F_USER_INACCESSIBLE) &&
> + (!PAGE_ALIGNED(offset) || !PAGE_ALIGNED(len))) {
> + error = -EINVAL;
> + goto out;
> + }
> +
> shmem_falloc.waitq = &shmem_falloc_waitq;
> shmem_falloc.start = (u64)unmap_start >> PAGE_SHIFT;
> shmem_falloc.next = (unmap_end + 1) >> PAGE_SHIFT;
> @@ -3806,6 +3850,20 @@ static int shmem_error_remove_page(struct address_space *mapping,
> return 0;
> }
>
> +#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?

> +}
> +#endif
> +
> const struct address_space_operations shmem_aops = {
> .writepage = shmem_writepage,
> .dirty_folio = noop_dirty_folio,
> @@ -3814,7 +3872,7 @@ const struct address_space_operations shmem_aops = {
> .write_end = shmem_write_end,
> #endif
> #ifdef CONFIG_MIGRATION
> - .migratepage = migrate_page,
> + .migratepage = shmem_migrate_page,
> #endif
> .error_remove_page = shmem_error_remove_page,
> };
> @@ -3931,6 +3989,51 @@ static struct file_system_type shmem_fs_type = {
> .fs_flags = FS_USERNS_MOUNT,
> };
>
> +#ifdef CONFIG_MEMFILE_NOTIFIER
> +static struct memfile_node *shmem_lookup_memfile_node(struct file *file)
> +{
> + struct inode *inode = file_inode(file);
> +
> + if (!shmem_mapping(inode->i_mapping))
> + return NULL;
> +
> + return &SHMEM_I(inode)->memfile_node;
> +}
> +
> +
> +static int shmem_get_pfn(struct file *file, pgoff_t offset, pfn_t *pfn,
> + int *order)
> +{
> + struct page *page;
> + int ret;
> +
> + ret = shmem_getpage(file_inode(file), offset, &page, SGP_WRITE);
> + if (ret)
> + return ret;
> +
> + unlock_page(page);
> + *pfn = page_to_pfn_t(page);
> + *order = thp_order(compound_head(page));
> + return 0;
> +}
> +
> +static void shmem_put_pfn(pfn_t pfn)
> +{
> + struct page *page = pfn_t_to_page(pfn);
> +
> + if (!page)
> + return;
> +
> + put_page(page);
> +}
> +
> +static struct memfile_backing_store shmem_backing_store = {
> + .lookup_memfile_node = shmem_lookup_memfile_node,
> + .get_pfn = shmem_get_pfn,
> + .put_pfn = shmem_put_pfn,
> +};
> +#endif /* CONFIG_MEMFILE_NOTIFIER */
> +
> void __init shmem_init(void)
> {
> int error;
> @@ -3956,6 +4059,10 @@ void __init shmem_init(void)
> else
> shmem_huge = SHMEM_HUGE_NEVER; /* just in case it was patched */
> #endif
> +
> +#ifdef CONFIG_MEMFILE_NOTIFIER
> + memfile_register_backing_store(&shmem_backing_store);
> +#endif
> return;
>
> out1: