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

[Jaegeuk Kim <jaegeuk@kernel.org>]

On 12/09, Eric Biggers wrote:
> On Mon, Dec 09, 2019 at 02:48:57PM -0800, Jaegeuk Kim wrote:
> > On 12/09, Eric Biggers wrote:
> > > 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.
> > 
> > I meant to ask why not just checking f2fs_post_read_required() here so that we
> > could sync the check across multiple places.
> > 
> 
> We can't use f2fs_post_read_required() here because f2fs_post_read_required()
> deals with a specific inode, but do_checkpoint() is dealing with the entire
> filesystem.  It's checking whether the filesystem might have *any* files that
> were moved via META_MAPPING.

Ah, I misread the code. Thank you for refreshing me.

> 
> - Eric


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