Commit 2c8951ab authored Jun 08, 2011 by Will Deacon

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: Dave Martin <dave.martin@linaro.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

parent 1a4baafa

arch/arm/mm/idmap.c

+10 −9

Original line number	Diff line number	Diff line
		@@ -100,17 +100,18 @@ static int __init init_static_idmap(void)
		arch_initcall(init_static_idmap);

		/*
		* 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. */
		flush_cache_all();

		/* Switch to the identity mapping. */
		cpu_switch_mm(idmap_pgd, &init_mm);

		/* Flush the TLB. */
		local_flush_tlb_all();
		}