Re: [f2fs-dev] [PATCH] f2fs: don't keep META_MAPPING pages used for moving verity file blocks

[Eric Biggers <ebiggers@kernel.org>]

On Mon, Dec 09, 2019 at 02:28:28PM -0800, Jaegeuk Kim wrote:
> On 12/09, Eric Biggers wrote:
> > From: Eric Biggers <ebiggers@google.com>
> > 
> > META_MAPPING is used to move blocks for both encrypted and verity files.
> > So the META_MAPPING invalidation condition in do_checkpoint() should
> > consider verity too, not just encrypt.
> > 
> > Signed-off-by: Eric Biggers <ebiggers@google.com>
> > ---
> >  fs/f2fs/checkpoint.c | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> > 
> > diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> > index ffdaba0c55d29..44e84ac5c9411 100644
> > --- a/fs/f2fs/checkpoint.c
> > +++ b/fs/f2fs/checkpoint.c
> > @@ -1509,10 +1509,10 @@ static int do_checkpoint(struct f2fs_sb_info *sbi, struct cp_control *cpc)
> >  	f2fs_wait_on_all_pages_writeback(sbi);
> >  
> >  	/*
> > -	 * invalidate intermediate page cache borrowed from meta inode
> > -	 * which are used for migration of encrypted inode's blocks.
> > +	 * invalidate intermediate page cache borrowed from meta inode which are
> > +	 * used for migration of encrypted or verity inode's blocks.
> >  	 */
> > -	if (f2fs_sb_has_encrypt(sbi))
> > +	if (f2fs_sb_has_encrypt(sbi) || f2fs_sb_has_verity(sbi))
> 
> Do we need f2fs_post_read_required() aligned to the condition of
> move_data_block()?
> 

I think you're asking why verity files have to be moved via META_MAPPING?  The
reason is that we have to be super careful not to read pages of a verity file
into its own address_space without doing the fs-verity data verification, as
then unverified data would be available to userspace.

In theory, F2FS's garbage collector could do the data verification.  But it's
tricky because ->i_verity_info may not have been set up yet.  So it might be
easiest to continue to treat verity files like encrypted files.

- Eric


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