Re: [PATCH] mm/page_table_check: Fix crash on ZONE_DEVICE

[Peter Xu <peterx@redhat.com>]

On Wed, Jun 05, 2024 at 03:05:43PM -0700, Andrew Morton wrote:
> On Wed,  5 Jun 2024 17:21:46 -0400 Peter Xu <peterx@redhat.com> wrote:
> 
> > Not all pages may apply to pgtable check.  One example is ZONE_DEVICE
> > pages: they map PFNs directly, and they don't allocate page_ext at all even
> > if there's struct page around.  One may reference devm_memremap_pages().
> > 
> > When both ZONE_DEVICE and page-table-check enabled, then try to map some
> > dax memories, one can trigger kernel bug constantly now when the kernel was
> > trying to inject some pfn maps on the dax device:
> > 
> >  kernel BUG at mm/page_table_check.c:55!
> > 
> > While it's pretty legal to use set_pxx_at() for ZONE_DEVICE pages for page
> > fault resolutions, skip all the checks if page_ext doesn't even exist in
> > pgtable checker, which applies to ZONE_DEVICE but maybe more.
> 
> Do we have a Reported-by: for this one?

Nop, I just hit that when I started to look at the dax issues.

> 
> And a Fixes?  It looks like df4e817b7108?

Yes that commit should be proper.

Thanks,

-- 
Peter Xu