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Date:   Tue, 9 May 2023 21:42:44 -0700 (PDT)
From:   Hugh Dickins <hughd@google.com>
To:     Andrew Morton <akpm@linux-foundation.org>
cc:     Mike Kravetz <mike.kravetz@oracle.com>,
        Mike Rapoport <rppt@kernel.org>,
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Subject: [PATCH 01/23] arm: allow pte_offset_map[_lock]() to fail
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In rare transient cases, not yet made possible, pte_offset_map() and
pte_offset_map_lock() may not find a page table: handle appropriately.

Signed-off-by: Hugh Dickins <hughd@google.com>
---
 arch/arm/lib/uaccess_with_memcpy.c | 3 +++
 arch/arm/mm/fault-armv.c           | 5 ++++-
 arch/arm/mm/fault.c                | 3 +++
 3 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/arm/lib/uaccess_with_memcpy.c b/arch/arm/lib/uaccess_with_memcpy.c
index e4c2677cc1e9..2f6163f05e93 100644
--- a/arch/arm/lib/uaccess_with_memcpy.c
+++ b/arch/arm/lib/uaccess_with_memcpy.c
@@ -74,6 +74,9 @@ pin_page_for_write(const void __user *_addr, pte_t **ptep, spinlock_t **ptlp)
 		return 0;
 
 	pte = pte_offset_map_lock(current->mm, pmd, addr, &ptl);
+	if (unlikely(!pte))
+		return 0;
+
 	if (unlikely(!pte_present(*pte) || !pte_young(*pte) ||
 	    !pte_write(*pte) || !pte_dirty(*pte))) {
 		pte_unmap_unlock(pte, ptl);
diff --git a/arch/arm/mm/fault-armv.c b/arch/arm/mm/fault-armv.c
index 0e49154454a6..ca5302b0b7ee 100644
--- a/arch/arm/mm/fault-armv.c
+++ b/arch/arm/mm/fault-armv.c
@@ -117,8 +117,11 @@ static int adjust_pte(struct vm_area_struct *vma, unsigned long address,
 	 * must use the nested version.  This also means we need to
 	 * open-code the spin-locking.
 	 */
-	ptl = pte_lockptr(vma->vm_mm, pmd);
 	pte = pte_offset_map(pmd, address);
+	if (!pte)
+		return 0;
+
+	ptl = pte_lockptr(vma->vm_mm, pmd);
 	do_pte_lock(ptl);
 
 	ret = do_adjust_pte(vma, address, pfn, pte);
diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
index 2418f1efabd8..83598649a094 100644
--- a/arch/arm/mm/fault.c
+++ b/arch/arm/mm/fault.c
@@ -85,6 +85,9 @@ void show_pte(const char *lvl, struct mm_struct *mm, unsigned long addr)
 			break;
 
 		pte = pte_offset_map(pmd, addr);
+		if (!pte)
+			break;
+
 		pr_cont(", *pte=%08llx", (long long)pte_val(*pte));
 #ifndef CONFIG_ARM_LPAE
 		pr_cont(", *ppte=%08llx",
-- 
2.35.3