Re: [PATCH v3 29/30] luo: allow preserving memfd

On 2025-08-07 01:44:35, Pasha Tatashin wrote:

From: Pratyush Yadav <redacted>
+static void memfd_luo_unpreserve_folios(const struct memfd_luo_preserved_folio *pfolios,
+					unsigned int nr_folios)
+{
+	unsigned int i;
+
+	for (i = 0; i < nr_folios; i++) {
+		const struct memfd_luo_preserved_folio *pfolio = &pfolios[i];
+		struct folio *folio;
+
+		if (!pfolio->foliodesc)
+			continue;
+
+		folio = pfn_folio(PRESERVED_FOLIO_PFN(pfolio->foliodesc));
+
+		kho_unpreserve_folio(folio);

This one is missing WARN_ON_ONCE() similar to the one in
memfd_luo_preserve_folios().

+		unpin_folio(folio);
+	}
+}
+
+static void *memfd_luo_create_fdt(unsigned long size)
+{
+	unsigned int order = get_order(size);
+	struct folio *fdt_folio;
+	int err = 0;
+	void *fdt;
+
+	if (order > MAX_PAGE_ORDER)
+		return NULL;
+
+	fdt_folio = folio_alloc(GFP_KERNEL, order);

__GFP_ZERO should also be used here. Otherwise this can lead to
unintentional passing of old kernel memory.

+static int memfd_luo_prepare(struct liveupdate_file_handler *handler,
+			     struct file *file, u64 *data)
+{
+	struct memfd_luo_preserved_folio *preserved_folios;
+	struct inode *inode = file_inode(file);
+	unsigned int max_folios, nr_folios = 0;
+	int err = 0, preserved_size;
+	struct folio **folios;
+	long size, nr_pinned;
+	pgoff_t offset;
+	void *fdt;
+	u64 pos;
+
+	if (WARN_ON_ONCE(!shmem_file(file)))
+		return -EINVAL;

This one is only check for shmem_file, whereas in
memfd_luo_can_preserve() there is check for inode->i_nlink also. Is that
not needed here?

+
+	inode_lock(inode);
+	shmem_i_mapping_freeze(inode, true);
+
+	size = i_size_read(inode);
+	if ((PAGE_ALIGN(size) / PAGE_SIZE) > UINT_MAX) {
+		err = -E2BIG;
+		goto err_unlock;
+	}
+
+	/*
+	 * Guess the number of folios based on inode size. Real number might end
+	 * up being smaller if there are higher order folios.
+	 */
+	max_folios = PAGE_ALIGN(size) / PAGE_SIZE;
+	folios = kvmalloc_array(max_folios, sizeof(*folios), GFP_KERNEL);

__GFP_ZERO?

+static int memfd_luo_freeze(struct liveupdate_file_handler *handler,
+			    struct file *file, u64 *data)
+{
+	u64 pos = file->f_pos;
+	void *fdt;
+	int err;
+
+	if (WARN_ON_ONCE(!*data))
+		return -EINVAL;
+
+	fdt = phys_to_virt(*data);
+
+	/*
+	 * The pos or size might have changed since prepare. Everything else
+	 * stays the same.
+	 */
+	err = fdt_setprop(fdt, 0, "pos", &pos, sizeof(pos));
+	if (err)
+		return err;

Comment is talking about pos and size but code is only updating pos. 

+static int memfd_luo_retrieve(struct liveupdate_file_handler *handler, u64 data,
+			      struct file **file_p)
+{
+	const struct memfd_luo_preserved_folio *pfolios;
+	int nr_pfolios, len, ret = 0, i = 0;
+	struct address_space *mapping;
+	struct folio *folio, *fdt_folio;
+	const u64 *pos, *size;
+	struct inode *inode;
+	struct file *file;
+	const void *fdt;
+
+	fdt_folio = memfd_luo_get_fdt(data);
+	if (!fdt_folio)
+		return -ENOENT;
+
+	fdt = page_to_virt(folio_page(fdt_folio, 0));
+
+	pfolios = fdt_getprop(fdt, 0, "folios", &len);
+	if (!pfolios || len % sizeof(*pfolios)) {
+		pr_err("invalid 'folios' property\n");

Print should clearly state that error is because fields is not found or
len is not multiple of sizeof(*pfolios).