Re: [PATCH] iomap: Add missing flush_dcache_page

[Matthew Wilcox <willy@infradead.org>]

On Fri, Jul 16, 2021 at 04:04:18PM +0100, Christoph Hellwig wrote:
> On Fri, Jul 16, 2021 at 04:00:32PM +0100, Matthew Wilcox (Oracle) wrote:
> > Inline data needs to be flushed from the kernel's view of a page before
> > it's mapped by userspace.
> > 
> > Cc: stable@vger.kernel.org
> > Fixes: 19e0c58f6552 ("iomap: generic inline data handling")
> > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> > ---
> >  fs/iomap/buffered-io.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> > index 41da4f14c00b..fe60c603f4ca 100644
> > --- a/fs/iomap/buffered-io.c
> > +++ b/fs/iomap/buffered-io.c
> > @@ -222,6 +222,7 @@ iomap_read_inline_data(struct inode *inode, struct page *page,
> >  	memcpy(addr, iomap->inline_data, size);
> >  	memset(addr + size, 0, PAGE_SIZE - size);
> >  	kunmap_atomic(addr);
> > +	flush_dcache_page(page);
> 
> .. and all writes into a kmap also need such a flush, so this needs to
> move a line up.  My plan was to add a memcpy_to_page_and_pad helper
> ala memcpy_to_page to get various file systems and drivers out of the
> business of cache flushing as much as we can.

hm?  It's absolutely allowed to flush the page after calling kunmap.
Look at zero_user_segments(), for example.