[PATCH] ARM: hibernate: flush TLB after switching to idmap

[Chongchong Ding]

On 32-bit ARM, hibernate switches to the identity mapping to copy pages.
The idmap keeps an early RW snapshot of kernel mappings, so
STRICT_KERNEL_RWX text/rodata can be written during restore.

cpu_switch_mm() does not drop the global TLB entries from swapper.
copy_page() can therefore still hit the old RO translations and fail to
restore kernel RO sections.

Flush the local BTB and TLB after installing the idmap, matching
setup_mm_for_reboot() and the cpu_suspend() resume path.

Signed-off-by: Chongchong Ding <chongchong.ding@xxxxxxxxxxx>
---
arch/arm/kernel/hibernate.c is only compiled when CONFIG_HIBERNATION is
enabled, and none of the 32-bit ARM defconfigs enable it, so the ARM
hibernation code has never been covered by the regular build tests.  This
bug was found while enabling the option for build coverage.
---
 arch/arm/kernel/hibernate.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/arm/kernel/hibernate.c b/arch/arm/kernel/hibernate.c
index 231a76af09a0..1c7c1cb6dade 100644
--- a/arch/arm/kernel/hibernate.c
+++ b/arch/arm/kernel/hibernate.c
@@ -21,6 +21,7 @@
 #include <asm/suspend.h>
 #include <asm/page.h>
 #include <asm/sections.h>
+#include <asm/tlbflush.h>
 #include <asm/uaccess.h>
 #include "reboot.h"
 
@@ -93,6 +94,17 @@ static void notrace arch_restore_image(void *unused)
 	if (IS_ENABLED(CONFIG_CPU_TTBR0_PAN))
 		uaccess_save_and_enable();
 	cpu_switch_mm(idmap_pgd, &init_mm);
+	local_flush_bp_all();
+
+#ifdef CONFIG_CPU_HAS_ASID
+	/*
+	 * The identity mapping has no clean ASID and may clash with entries
+	 * left behind by the previous page tables.  Without this flush,
+	 * copy_page() can translate through the stale read-only kernel
+	 * mappings instead of the writable aliases in the idmap.
+	 */
+	local_flush_tlb_all();
+#endif
 	for (pbe = restore_pblist; pbe; pbe = pbe->next)
 		copy_page(pbe->orig_address, pbe->address);
 

---
base-commit: 551c722f40809618230001baccf219193e22fc5a
change-id: 20260928-hibernate-tlb-flush-f2c1c5315625

Best regards,
--  
Chongchong Ding <chongchong.ding@xxxxxxxxxxx>