Re: [PATCH v14 05/21] fsverity: improve flushing performance of fsverity_fill_zerohash

On Tue, Aug 04, 2026 at 07:46:03PM +0100, Matthew Wilcox wrote:
> On Mon, Aug 03, 2026 at 10:07:55PM +0200, Andrey Albershteyn wrote:
> > The current version calls flush_dcache_folio(), in memcpy_to_folio(), to
> > flush whole folio on every digest (which is 128 for 4k) on the HIGHMEM
> > systems. Open code folio mapping and flushing to copy all digests at
> > once.
> 
> Have you looked at the implementations of flush_dcache_folio()?  On
> any architecture we actually care about, all it does is set one bit
> in folio->flags noting that the folio will need to be flushed if
> it's going to be accessed by userspace.
> 
> But, um, do we support mapping folios containing fsverity data into
> userspace?  Can't we just delete the calls to flush_dcache_folio()?

I don't think programs are allowed to mmap the fsverity data, right?
I know there's an ioctl that effectively allows read()ing it.

--D