linux-kernel - [PATCH] arm64: Check pxd_leaf() instead of !pxd

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Message-Id: <20250515063450.86629-1-dev.jain@arm.com>
Date: Thu, 15 May 2025 12:04:50 +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] arm64: Check pxd_leaf() instead of !pxd_table() while tearing down page tables

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, enforce
these checks again through pxd_leaf().
This problem was found by code inspection.
The 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>
---
 arch/arm64/mm/mmu.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index ea6695d53fb9..3d6789413a9b 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -1255,7 +1255,7 @@ int pmd_free_pte_page(pmd_t *pmdp, unsigned long addr)
 
 	pmd = READ_ONCE(*pmdp);
 
-	if (!pmd_table(pmd)) {
+	if (pmd_leaf(pmd)) {
 		VM_WARN_ON(1);
 		return 1;
 	}
@@ -1276,7 +1276,7 @@ int pud_free_pmd_page(pud_t *pudp, unsigned long addr)
 
 	pud = READ_ONCE(*pudp);
 
-	if (!pud_table(pud)) {
+	if (pud_leaf(pud)) {
 		VM_WARN_ON(1);
 		return 1;
 	}
-- 
2.30.2