[PATCH 2/4] mm/huge_memory: skip zone device folios in madvise_free_huge_pmd()

madvise_free_huge_pmd() resolves the folio backing a PMD via pmd_folio()
and marks it lazyfree without checking for zone device memory.

The surrounding guards do not cover every zone device case:
 - MADV_FREE only operates on anonymous VMAs (DAX mappings are excluded)

 - !pmd_present() branch rejects device-private and migration entries

 - present zone device PMD (device coherent THP) is not filtered.
   Unlike vm_normal_page_pmd(), it performs no special/pfnmap check,
   and would be marked lazyfree here.

Bail out when the folio is a zone device folio.

Fixes: 368076f52ebe ("mm/huge_memory: add device-private THP support to PMD operations")
Cc: <[email protected]>
Signed-off-by: Gregory Price (Meta) <[email protected]>
---
 mm/huge_memory.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 5bd8d4f59a7b..e0ffdeeb3077 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2338,6 +2338,10 @@ bool madvise_free_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
 	}
 
 	folio = pmd_folio(orig_pmd);
+
+	if (folio_is_zone_device(folio))
+		goto out;
+
 	/*
 	 * If other processes are mapping this folio, we couldn't discard
 	 * the folio unless they all do MADV_FREE so let's skip the folio.
-- 
2.55.0