Re: [PATCH RFC 01/14] mm/memory: drop highest_memmap_pfn sanity check in vm_normal_page()

[Oscar Salvador]

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 <david@xxxxxxxxxx>

I'm confused, I'm missing something here.
Before this change we would return NULL if e.g: pfn > highest_memmap_pfn, but
now we just print the warning and call pfn_to_page() anyway.
AFAIK, pfn_to_page() doesn't return NULL?
 

-- 
Oscar Salvador
SUSE Labs