linux-kernel - [v2 PATCH] arm64: mm: Fix kexec failure after pte_mkwrite

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Message-ID: <20251202022707.2720933-1-jianpeng.chang.cn@windriver.com>
Date: Tue, 2 Dec 2025 10:27:07 +0800
From: Jianpeng Chang <jianpeng.chang.cn@...driver.com>
To: <catalin.marinas@....com>, <will@...nel.org>, <ardb@...nel.org>,
        <anshuman.khandual@....com>, <ying.huang@...ux.alibaba.com>
CC: <jianpeng.chang.cn@...driver.com>, <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: [v2 PATCH] arm64: mm: Fix kexec failure after pte_mkwrite_novma() change

Commit 143937ca51cc ("arm64, mm: avoid always making PTE dirty in
pte_mkwrite()") modified pte_mkwrite_novma() to only clear PTE_RDONLY
when the page is already dirty (PTE_DIRTY is set). While this optimization
prevents unnecessary dirty page marking in normal memory management paths,
it breaks kexec on some platforms like NXP LS1043.

The issue occurs in the kexec code path:
1. machine_kexec_post_load() calls trans_pgd_create_copy() to create a
   writable copy of the linear mapping
2. _copy_pte() calls pte_mkwrite_novma() to ensure all pages in the copy
   are writable for the new kernel image copying
3. With the new logic, clean pages (without PTE_DIRTY) remain read-only
4. When kexec tries to copy the new kernel image through the linear
   mapping, it fails on read-only pages, causing the system to hang
   after "Bye!"

The same issue affects hibernation which uses the same trans_pgd code path.

Fix this by explicitly clearing PTE_RDONLY in _copy_pte() for both
kexec and hibernation, ensuring all pages in the temporary mapping are
writable regardless of their dirty state. This preserves the original
commit's optimization for normal memory management while fixing the
kexec/hibernation regression.

Fixes: 143937ca51cc ("arm64, mm: avoid always making PTE dirty in pte_mkwrite()")
Signed-off-by: Jianpeng Chang <jianpeng.chang.cn@...driver.com>
---
v2:
  - Use pte_mkwrite_novma(pte_mkdirty(pte)) instead of manual bit manipulation
  - Updated comments to clarify pte_mkwrite_novma() alone cannot be used
v1: https://lore.kernel.org/all/20251127034350.3600454-1-jianpeng.chang.cn@windriver.com/

 arch/arm64/mm/trans_pgd.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/mm/trans_pgd.c b/arch/arm64/mm/trans_pgd.c
index 18543b603c77..08f5ee6643e1 100644
--- a/arch/arm64/mm/trans_pgd.c
+++ b/arch/arm64/mm/trans_pgd.c
@@ -40,8 +40,13 @@ static void _copy_pte(pte_t *dst_ptep, pte_t *src_ptep, unsigned long addr)
 		 * Resume will overwrite areas that may be marked
 		 * read only (code, rodata). Clear the RDONLY bit from
 		 * the temporary mappings we use during restore.
+		 *
+		 * For kexec/hibernation, we need writable access to all
+		 * pages in the linear mapping to copy the new kernel image.
+		 * Mark pages dirty first to ensure pte_mkwrite_novma()
+		 * clears PTE_RDONLY.
 		 */
-		__set_pte(dst_ptep, pte_mkwrite_novma(pte));
+		__set_pte(dst_ptep, pte_mkwrite_novma(pte_mkdirty(pte)));
 	} else if (!pte_none(pte)) {
 		/*
 		 * debug_pagealloc will removed the PTE_VALID bit if
@@ -57,7 +62,7 @@ static void _copy_pte(pte_t *dst_ptep, pte_t *src_ptep, unsigned long addr)
 		 */
 		BUG_ON(!pfn_valid(pte_pfn(pte)));

-		__set_pte(dst_ptep, pte_mkvalid(pte_mkwrite_novma(pte)));
+		__set_pte(dst_ptep, pte_mkvalid(pte_mkwrite_novma(pte_mkdirty(pte))));
 	}
 }

-- 
2.51.2