[PATCH 5.15.y] arm64: Restrict pagetable teardown to avoid false warning

[Dev Jain <dev.jain@arm.com>]

[Commit 650768c512faba8070bf4cfbb28c95eb5cd203f3 upstream]

Commit 9c006972c3fe ("arm64: mmu: drop pXd_present() checks from
pXd_free_pYd_table()") removes the pxd_present() checks because the
caller checks pxd_present(). But, in case of vmap_try_huge_pud(), the
caller only checks pud_present(); pud_free_pmd_page() recurses on each
pmd through pmd_free_pte_page(), wherein the pmd may be none. Thus it is
possible to hit a warning in the latter, since pmd_none => !pmd_table().
Thus, add a pmd_present() check in pud_free_pmd_page().

This problem was found by code inspection.

Fixes: 9c006972c3fe ("arm64: mmu: drop pXd_present() checks from pXd_free_pYd_table()")
Cc: stable@vger.kernel.org
Reported-by: Ryan Roberts <ryan.roberts@arm.com>
Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Dev Jain <dev.jain@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
Link: https://lore.kernel.org/r/20250527082633.61073-1-dev.jain@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
(cherry picked from commit 650768c512faba8070bf4cfbb28c95eb5cd203f3)
(use READ_ONCE since pmdp_get() is not defined)
---
 arch/arm64/mm/mmu.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index fc86e7465df4..e3e4defdea42 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -1466,7 +1466,8 @@ int pud_free_pmd_page(pud_t *pudp, unsigned long addr)
 	next = addr;
 	end = addr + PUD_SIZE;
 	do {
-		pmd_free_pte_page(pmdp, next);
+		if (pmd_present(READ_ONCE(*pmdp)))
+			pmd_free_pte_page(pmdp, next);
 	} while (pmdp++, next += PMD_SIZE, next != end);
 
 	pud_clear(pudp);
-- 
2.30.2