Commit 2c8951ab authored by Will Deacon's avatar Will Deacon
Browse files

ARM: idmap: use idmap_pgd when setting up mm for reboot

For soft-rebooting a system, it is necessary to map the MMU-off code
with an identity mapping so that execution can continue safely once the
MMU has been switched off.

Currently, switch_mm_for_reboot takes out a 1:1 mapping from 0x0 to
TASK_SIZE during reboot in the hope that the reset code lives at a
physical address corresponding to a userspace virtual address.

This patch modifies the code so that we switch to the idmap_pgd tables,
which contain a 1:1 mapping of the cpu_reset code. This has the
advantage of only remapping the code that we need and also means we
don't need to worry about allocating a pgd from an atomic context in the
case that the physical address of the cpu_reset code aliases with the
virtual space used by the kernel.
Acked-by: default avatarDave Martin <>
Reviewed-by: default avatarCatalin Marinas <>
Signed-off-by: default avatarWill Deacon <>
parent 1a4baafa
......@@ -100,17 +100,18 @@ static int __init init_static_idmap(void)
* In order to soft-boot, we need to insert a 1:1 mapping in place of
* the user-mode pages. This will then ensure that we have predictable
* results when turning the mmu off
* In order to soft-boot, we need to switch to a 1:1 mapping for the
* cpu_reset functions. This will then ensure that we have predictable
* results when turning off the mmu.
void setup_mm_for_reboot(void)
* We need to access to user-mode page tables here. For kernel threads
* we don't have any user-mode mappings so we use the context that we
* "borrowed".
identity_mapping_add(current->active_mm->pgd, 0, TASK_SIZE);
/* Clean and invalidate L1. */
/* Switch to the identity mapping. */
cpu_switch_mm(idmap_pgd, &init_mm);
/* Flush the TLB. */
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