linux-kernel - [PATCH v2] arm64: Restrict pagetable teardown to avoid false warning

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Message-Id: <20250518095445.31044-1-dev.jain@arm.com>
Date: Sun, 18 May 2025 15:24:45 +0530
From: Dev Jain <dev.jain@....com>
To: catalin.marinas@....com,
	will@...nel.org
Cc: david@...hat.com,
	ryan.roberts@....com,
	anshuman.khandual@....com,
	mark.rutland@....com,
	yang@...amperecomputing.com,
	linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Dev Jain <dev.jain@....com>,
	stable@...r.kernel.org
Subject: [PATCH v2] arm64: Restrict pagetable teardown to avoid false warning

Commit 9c006972c3fe 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.

This patch is based on 6.15-rc6.

Fixes: 9c006972c3fe (arm64: mmu: drop pXd_present() checks from pXd_free_pYd_table())

Cc: <stable@...r.kernel.org>
Reported-by: Ryan Roberts <ryan.roberts@....com> 
Signed-off-by: Dev Jain <dev.jain@....com>
---
v1->v2:
 - Enforce check in caller

 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 ea6695d53fb9..5b1f4cd238ca 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -1286,7 +1286,8 @@ 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(*pmdp))
+			pmd_free_pte_page(pmdp, next);
 	} while (pmdp++, next += PMD_SIZE, next != end);
 
 	pud_clear(pudp);
-- 
2.30.2