Re: [PATCH v8 05/13] KVM: guest_memfd: Add flag to remove from direct map
From: Dave Hansen <hidden>
Date: 2025-12-05 17:30:15
Also in:
bpf, kvm, kvmarm, linux-fsdevel, linux-kselftest, linux-mm, lkml
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.