btrfs: concentrate highmem handling for data verification

Currently for btrfs checksum verification, we do it in the following
pattern:

	kaddr = kmap_local_*();
	ret = btrfs_check_csum_csum(kaddr);
	kunmap_local(kaddr);

It's OK for now, but it's still not following the patterns of helpers
inside linux/highmem.h, which never requires a virt memory address.

In those highmem helpers, they mostly accept a folio, some offset/length
inside the folio, and in the implementation they check if the folio
needs partial kmap, and do the handling.

Inspired by those formal highmem helpers, enhance the highmem handling
of data checksum verification by:

- Rename btrfs_check_sector_csum() to btrfs_check_block_csum()
  To follow the more common term "block" used in all other major
  filesystems.

- Pass a physical address into btrfs_check_block_csum() and
  btrfs_data_csum_ok()
  The physical address is always available even for a highmem page.
  Since it's page frame number << PAGE_SHIFT + offset in page.

  And with that physical address, we can grab the folio covering the
  page, and do extra checks to ensure it covers at least one block.

  This also allows us to do the kmap inside btrfs_check_block_csum().
  This means all the extra HIGHMEM handling will be concentrated into
  btrfs_check_block_csum(), and no callers will need to bother highmem
  by themselves.

- Properly zero out the block if csum mismatch
  Since btrfs_data_csum_ok() only got a paddr, we can not and should not
  use memzero_bvec(), which only accepts single page bvec.
  Instead use paddr to grab the folio and call folio_zero_range()

Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 16 insertions, 2 deletions

diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index 2f10c65929dc..cef260ed854c 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -696,6 +696,20 @@ static void *scrub_stripe_get_kaddr(struct scrub_stripe *stripe, int sector_nr)
 	return page_address(page) + offset_in_page(offset);
 }
 
+static phys_addr_t scrub_stripe_get_paddr(struct scrub_stripe *stripe, int sector_nr)
+{
+	struct btrfs_fs_info *fs_info = stripe->bg->fs_info;
+	u32 offset = (sector_nr << fs_info->sectorsize_bits);
+	const struct page *page = stripe->pages[offset >> PAGE_SHIFT];
+
+	/* stripe->pages[] is allocated by us and no highmem is allowed. */
+	ASSERT(page);
+	ASSERT(!PageHighMem(page));
+	/* And the range must be contained inside the page. */
+	ASSERT(offset_in_page(offset) + fs_info->sectorsize <= PAGE_SIZE);
+	return page_to_phys(page) + offset_in_page(offset);
+}
+
 static void scrub_verify_one_metadata(struct scrub_stripe *stripe, int sector_nr)
 {
 	struct btrfs_fs_info *fs_info = stripe->bg->fs_info;
@@ -788,7 +802,7 @@ static void scrub_verify_one_sector(struct scrub_stripe *stripe, int sector_nr)
 	struct btrfs_fs_info *fs_info = stripe->bg->fs_info;
 	struct scrub_sector_verification *sector = &stripe->sectors[sector_nr];
 	const u32 sectors_per_tree = fs_info->nodesize >> fs_info->sectorsize_bits;
-	void *kaddr = scrub_stripe_get_kaddr(stripe, sector_nr);
+	phys_addr_t paddr = scrub_stripe_get_paddr(stripe, sector_nr);
 	u8 csum_buf[BTRFS_CSUM_SIZE];
 	int ret;
 
@@ -833,7 +847,7 @@ static void scrub_verify_one_sector(struct scrub_stripe *stripe, int sector_nr)
 		return;
 	}
 
-	ret = btrfs_check_sector_csum(fs_info, kaddr, csum_buf, sector->csum);
+	ret = btrfs_check_block_csum(fs_info, paddr, csum_buf, sector->csum);
 	if (ret < 0) {
 		scrub_bitmap_set_bit_csum_error(stripe, sector_nr);
 		scrub_bitmap_set_bit_error(stripe, sector_nr);