On Fri, 4 Jul 2025, David Hildenbrand wrote:
> On 03.07.25 16:44, Lance Yang wrote:
> > On 2025/7/3 20:39, David Hildenbrand wrote:
> >> On 03.07.25 14:34, Lance Yang wrote:
> >>> On Mon, Jun 23, 2025 at 10:04 PM David Hildenbrand <da...@redhat.com>
> >>> wrote:
> >>>>
> >>>> On 20.06.25 14:50, Oscar Salvador wrote:
> >>>>> On Tue, Jun 17, 2025 at 05:43:32PM +0200, David Hildenbrand wrote:
> >>>>>> In 2009, we converted a VM_BUG_ON(!pfn_valid(pfn)) to the current
> >>>>>> highest_memmap_pfn sanity check in commit 22b31eec63e5 ("badpage:
> >>>>>> vm_normal_page use print_bad_pte"), because highest_memmap_pfn was
> >>>>>> readily available.
> >>>>>>
> >>>>>> Nowadays, this is the last remaining highest_memmap_pfn user, and this
> >>>>>> sanity check is not really triggering ... frequently.
> >>>>>>
> >>>>>> Let's convert it to VM_WARN_ON_ONCE(!pfn_valid(pfn)), so we can
> >>>>>> simplify and get rid of highest_memmap_pfn. Checking for
> >>>>>> pfn_to_online_page() might be even better, but it would not handle
> >>>>>> ZONE_DEVICE properly.
> >>>>>>
> >>>>>> Do the same in vm_normal_page_pmd(), where we don't even report a
> >>>>>> problem at all ...
> >>>>>>
> >>>>>> What might be better in the future is having a runtime option like
> >>>>>> page-table-check to enable such checks dynamically on-demand.
> >>>>>> Something
> >>>>>> for the future.
> >>>>>>
> >>>>>> Signed-off-by: David Hildenbrand <da...@redhat.com>The author of 22b31eec63e5 thinks this is not at all an improvement. Of course the condition is not triggering frequently, of course it should not happen: but it does happen, and it still seems worthwhile to catch it in production with a "Bad page map" than to let it run on to whatever kind of crash it hits instead. Hugh
