[PATCH v2] ARM: kexec: selective MMU identity mapping
Per Fransson
per.xx.fransson at stericsson.com
Wed Feb 2 09:43:29 EST 2011
When restarting using the kernel kexec functionality the MMU
needs to be turned off. Any code which does this needs to use
identity mapped addresses to get reliable results. In the ARM
kexec case this identity mapping is done:
- using the page table of the current task
- for all addresses normally used by user space,
i.e. 0x00000000-PAGE_OFFSET
If kexec is used at a kernel crash to collect a core dump this
means that we lose important information.
This is what this patches does:
* Actually turns off the MMU, which has been omitted by mistake
* Sets up a more selective identity mapping
* Restores the old mapping once the MMU is off
Signed-off-by: Per Fransson <per.xx.fransson at stericsson.com>
---
v2 changes:
* now uses (modified versions of) the identity mapping functions in idmap.c
as they look in 2.6.38-rc1. Some pud-level code has been added there in
linux-next.
arch/arm/include/asm/pgtable.h | 4 +++-
arch/arm/kernel/machine_kexec.c | 26 +++++++++++++++++++++-----
arch/arm/kernel/relocate_kernel.S | 23 +++++++++++++++++++++++
arch/arm/kernel/smp.c | 7 ++++---
arch/arm/mm/idmap.c | 20 +++++++++++++++-----
arch/arm/mm/proc-v7.S | 4 ++++
include/linux/kexec.h | 6 +++++-
7 files changed, 75 insertions(+), 15 deletions(-)
diff --git a/arch/arm/include/asm/pgtable.h b/arch/arm/include/asm/pgtable.h
index ebcb643..08dd591 100644
--- a/arch/arm/include/asm/pgtable.h
+++ b/arch/arm/include/asm/pgtable.h
@@ -458,6 +458,7 @@ static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
#define kern_addr_valid(addr) (1)
#include <asm-generic/pgtable.h>
+#include <linux/kexec.h>
/*
* We provide our own arch_get_unmapped_area to cope with VIPT caches.
@@ -473,7 +474,8 @@ static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
#define pgtable_cache_init() do { } while (0)
-void identity_mapping_add(pgd_t *, unsigned long, unsigned long);
+void identity_mapping_add(pgd_t *, unsigned long, unsigned long,
+ struct kexec_mmu_ent *);
void identity_mapping_del(pgd_t *, unsigned long, unsigned long);
#endif /* !__ASSEMBLY__ */
diff --git a/arch/arm/kernel/machine_kexec.c b/arch/arm/kernel/machine_kexec.c
index 30ead13..bd53684 100644
--- a/arch/arm/kernel/machine_kexec.c
+++ b/arch/arm/kernel/machine_kexec.c
@@ -16,8 +16,6 @@
extern const unsigned char relocate_new_kernel[];
extern const unsigned int relocate_new_kernel_size;
-extern void setup_mm_for_reboot(char mode);
-
extern unsigned long kexec_start_address;
extern unsigned long kexec_indirection_page;
extern unsigned long kexec_mach_type;
@@ -79,9 +77,9 @@ void machine_kexec(struct kimage *image)
{
unsigned long page_list;
unsigned long reboot_code_buffer_phys;
+ unsigned long cpu_reset_phys;
void *reboot_code_buffer;
-
page_list = image->head & PAGE_MASK;
/* we need both effective and real address here */
@@ -95,18 +93,36 @@ void machine_kexec(struct kimage *image)
kexec_mach_type = machine_arch_type;
kexec_boot_atags = image->start - KEXEC_ARM_ZIMAGE_OFFSET + KEXEC_ARM_ATAGS_OFFSET;
+ /* Identity map the code which turns off the mmu (cpu_reset) and
+ the code which will be executed immediately afterwards
+ (relocate_new_kernel).
+ Store the old entries so they can be restored. */
+ /* cpu_reset cannot be used directly when MULTI_CPU is true, see
+ cpu-multi32.h, instead processor.reset will have to be used */
+#ifdef MULTI_CPU
+ cpu_reset_phys = virt_to_phys(processor.reset);
+#else
+ cpu_reset_phys = virt_to_phys(cpu_reset);
+#endif
+
+ identity_mapping_add(current->active_mm->pgd, cpu_reset_phys,
+ ALIGN(cpu_reset_phys, PGDIR_SIZE)+PGDIR_SIZE,
+ &kexec_mmu_ents[0]);
+ identity_mapping_add(current->active_mm->pgd, reboot_code_buffer_phys,
+ ALIGN(reboot_code_buffer_phys, PGDIR_SIZE)
+ + PGDIR_SIZE, &kexec_mmu_ents[2]);
+ local_flush_tlb_all();
+
/* copy our kernel relocation code to the control code page */
memcpy(reboot_code_buffer,
relocate_new_kernel, relocate_new_kernel_size);
-
flush_icache_range((unsigned long) reboot_code_buffer,
(unsigned long) reboot_code_buffer + KEXEC_CONTROL_PAGE_SIZE);
printk(KERN_INFO "Bye!\n");
local_irq_disable();
local_fiq_disable();
- setup_mm_for_reboot(0); /* mode is not used, so just pass 0*/
flush_cache_all();
outer_flush_all();
outer_disable();
diff --git a/arch/arm/kernel/relocate_kernel.S b/arch/arm/kernel/relocate_kernel.S
index 9cf4cbf..a5e155e 100644
--- a/arch/arm/kernel/relocate_kernel.S
+++ b/arch/arm/kernel/relocate_kernel.S
@@ -7,6 +7,24 @@
.globl relocate_new_kernel
relocate_new_kernel:
+ /* We get here when the MMU is in a transitional state.
+ Wait for the virtual address mapping to wear off before
+ overwriting the identity mappings (set up for the sake
+ of MMU disabling) with the previous mappings. */
+ ldr r0, =100
+0:
+ subs r0, r0, #1
+ beq 0b
+
+ adr r0, kexec_mmu_ents
+ .rept 4
+ ldr r1, [r0], #4
+ ldr r2, [r0], #4
+ str r2, [r1], #4
+ ldr r2, [r0], #4
+ str r2, [r1], #4
+ .endr
+
ldr r0,kexec_indirection_page
ldr r1,kexec_start_address
@@ -69,6 +87,11 @@ kexec_start_address:
kexec_indirection_page:
.long 0x0
+ .globl kexec_mmu_ents
+kexec_mmu_ents:
+ .space 4*12, 0
+
+
.globl kexec_mach_type
kexec_mach_type:
.long 0x0
diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index 4539ebc..607b6a8 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -93,10 +93,11 @@ int __cpuinit __cpu_up(unsigned int cpu)
if (PHYS_OFFSET != PAGE_OFFSET) {
#ifndef CONFIG_HOTPLUG_CPU
- identity_mapping_add(pgd, __pa(__init_begin), __pa(__init_end));
+ identity_mapping_add(pgd, __pa(__init_begin), __pa(__init_end),
+ NULL);
#endif
- identity_mapping_add(pgd, __pa(_stext), __pa(_etext));
- identity_mapping_add(pgd, __pa(_sdata), __pa(_edata));
+ identity_mapping_add(pgd, __pa(_stext), __pa(_etext), NULL);
+ identity_mapping_add(pgd, __pa(_sdata), __pa(_edata), NULL);
}
/*
diff --git a/arch/arm/mm/idmap.c b/arch/arm/mm/idmap.c
index 5729944..d5d313d 100644
--- a/arch/arm/mm/idmap.c
+++ b/arch/arm/mm/idmap.c
@@ -1,14 +1,19 @@
#include <linux/kernel.h>
+#include <linux/kexec.h>
#include <asm/cputype.h>
#include <asm/pgalloc.h>
#include <asm/pgtable.h>
static void idmap_add_pmd(pgd_t *pgd, unsigned long addr, unsigned long end,
- unsigned long prot)
+ unsigned long prot, struct kexec_mmu_ent *store)
{
pmd_t *pmd = pmd_offset(pgd, addr);
-
+ if (store) {
+ pmd_t *pmd_store = pmd_offset(&store->store, addr);
+ pmd_store[0] = pmd[0];
+ pmd_store[1] = pmd[1];
+ }
addr = (addr & PMD_MASK) | prot;
pmd[0] = __pmd(addr);
addr += SECTION_SIZE;
@@ -16,7 +21,8 @@ static void idmap_add_pmd(pgd_t *pgd, unsigned long addr, unsigned long end,
flush_pmd_entry(pmd);
}
-void identity_mapping_add(pgd_t *pgd, unsigned long addr, unsigned long end)
+void identity_mapping_add(pgd_t *pgd, unsigned long addr, unsigned long end,
+ struct kexec_mmu_ent *store)
{
unsigned long prot, next;
@@ -27,7 +33,11 @@ void identity_mapping_add(pgd_t *pgd, unsigned long addr, unsigned long end)
pgd += pgd_index(addr);
do {
next = pgd_addr_end(addr, end);
- idmap_add_pmd(pgd, addr, next, prot);
+ idmap_add_pmd(pgd, addr, next, prot, store);
+ if (store) {
+ store->ptr = (pgd_t *)virt_to_phys(pgd);
+ store++;
+ }
} while (pgd++, addr = next, addr != end);
}
@@ -62,6 +72,6 @@ void setup_mm_for_reboot(char mode)
* 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);
+ identity_mapping_add(current->active_mm->pgd, 0, TASK_SIZE, NULL);
local_flush_tlb_all();
}
diff --git a/arch/arm/mm/proc-v7.S b/arch/arm/mm/proc-v7.S
index 0c1172b..762bb43 100644
--- a/arch/arm/mm/proc-v7.S
+++ b/arch/arm/mm/proc-v7.S
@@ -61,6 +61,10 @@ ENDPROC(cpu_v7_proc_fin)
*/
.align 5
ENTRY(cpu_v7_reset)
+ sub pc, pc, #PAGE_OFFSET+4 @ go to physical addresses
+ mrc p15, 0, ip, c1, c0, 0 @ ctrl register
+ bic ip, ip, #0x0001 @ ...............m
+ mcr p15, 0, ip, c1, c0, 0 @ ctrl register
mov pc, r0
ENDPROC(cpu_v7_reset)
diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index 03e8e8d..6a1345b 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -106,7 +106,11 @@ struct kimage {
#endif
};
-
+struct kexec_mmu_ent {
+ pgd_t *ptr;
+ pgd_t store;
+};
+extern struct kexec_mmu_ent kexec_mmu_ents[4];
/* kexec interface functions */
extern void machine_kexec(struct kimage *image);
--
1.7.3.2
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