Re: [PATCH v8 05/13] KVM: guest_memfd: Add flag to remove from direct map

On 12/5/25 08:58, Kalyazin, Nikita wrote:

+static void kvm_gmem_folio_restore_direct_map(struct folio *folio) +{

• /*

• * Direct map restoration cannot fail, as the only error condition
  

• * for direct map manipulation is failure to allocate page tables
  

• * when splitting huge pages, but this split would have already
  

• * happened in set_direct_map_invalid_noflush() in kvm_gmem_folio_zap_direct_map().
  

• * Thus set_direct_map_valid_noflush() here only updates prot bits.
  

• */
  

• if (kvm_gmem_folio_no_direct_map(folio))

• set_direct_map_valid_noflush(folio_page(folio, 0), folio_nr_pages(folio),
  

• 			 true);
  

+}

This is rather hopeful programming.

I can think of a number of ways that this assumption might become invalid. This at *least* check for set_direct_map_valid_noflush() failures (or whatever interface you end up using)?

A WARN_ON_ONCE() would be fine.