On Thu, Jan 26, 2023 at 08:48:03PM +0000, Matthew Wilcox wrote: > On Thu, Jan 26, 2023 at 12:38:58PM -0800, Andrew Morton wrote: > > On Thu, 26 Jan 2023 15:33:46 +0100 "Fabio M. De Francesco" <fmdefrancesco@xxxxxxxxx> wrote: > > > > > If ARCH_HAS_FLUSH_ON_KUNMAP is defined (PA-RISC case), __kunmap_local() > > > calls kunmap_flush_on_unmap(). The latter currently flushes the wrong > > > address (as confirmed by Matthew Wilcox and Helge Deller). Al Viro > > > proposed to call kunmap_flush_on_unmap() on an aligned-down to page > > > address in order to fix this issue. Consensus has been reached on this > > > solution. > > > > What are the user-visible runtime effects of this flaw? > > The version of this patch I sent out includes this information, > as well as the missed alignment for kunmap_atomic(). One point: AFAICS, the situation right now is * all callers of kunmap_local() pass page-aligned pointers * all callers of kunmap_atomic() seem to do the same * there's nothing in documentation that would say one can pass anything other than the return value of original kmap_local_page() or kmap_atomic() call to those. * there's nothing that would outright ban doing that. So these patches really ought to touch Documentation/mm/highmem.rst saying that from now on kunmap_local() and kunmap_atomic() callers are allowed to pass any pointer within the mapped area. And yes, we want it in -stable before anything that relies upon that sucker gets backported.
