[PATCH 1/4] ARM: catch pending imprecise abort on unmask

[Lucas Stach <l.stach@xxxxxxxxxxxxxx>]

Install a non-faulting handler just before unmasking imprecise aborts
and switch back to the regular one after unmasking is done.

This catches any pending imprecise abort that the firmware/bootloader
may have left behind that would normally crash the kernel at that point.
As there are apparently a lot of bootlaoders out there that do such a
thing it makes sense to handle it in the common startup code.

Signed-off-by: Lucas Stach <l.stach@xxxxxxxxxxxxxx>
---
 arch/arm/mm/fault.c | 15 +++++++++++++++
 arch/arm/mm/fault.h |  2 ++
 arch/arm/mm/mmu.c   | 19 ++++++++++++++++++-
 3 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
index 0d629b8f973f..519f694ec9db 100644
--- a/arch/arm/mm/fault.c
+++ b/arch/arm/mm/fault.c
@@ -538,6 +538,21 @@ hook_fault_code(int nr, int (*fn)(unsigned long, unsigned int, struct pt_regs *)
 	fsr_info[nr].name = name;
 }
 
+void * __init
+swap_fault_function(int nr,
+		    int (*fn)(unsigned long, unsigned int, struct pt_regs *))
+{
+	void *old_fn;
+
+	if (nr < 0 || nr >= ARRAY_SIZE(fsr_info))
+		BUG();
+
+	old_fn = fsr_info[nr].fn;
+	fsr_info[nr].fn = fn;
+
+	return old_fn;
+}
+
 /*
  * Dispatch a data abort to the relevant handler.
  */
diff --git a/arch/arm/mm/fault.h b/arch/arm/mm/fault.h
index cf08bdfbe0d6..2deb7494d84f 100644
--- a/arch/arm/mm/fault.h
+++ b/arch/arm/mm/fault.h
@@ -24,5 +24,7 @@ static inline int fsr_fs(unsigned int fsr)
 
 void do_bad_area(unsigned long addr, unsigned int fsr, struct pt_regs *regs);
 unsigned long search_exception_table(unsigned long addr);
+void *swap_fault_function(int nr,
+		int (*fn)(unsigned long, unsigned int, struct pt_regs *));
 
 #endif	/* __ARCH_ARM_FAULT_H */
diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
index f65a6f344b6d..78c420776f4c 100644
--- a/arch/arm/mm/mmu.c
+++ b/arch/arm/mm/mmu.c
@@ -38,6 +38,7 @@
 #include <asm/mach/pci.h>
 #include <asm/fixmap.h>
 
+#include "fault.h"
 #include "mm.h"
 #include "tcm.h"
 
@@ -1259,6 +1260,20 @@ void __init arm_mm_memblock_reserve(void)
 }
 
 /*
+ * Abort handler to be used only during unmasking of imprecise aborts. This
+ * makes sure that the machine will not die if the firmware/bootloader left an
+ * imprecise abort pending for us to trip over.
+ */
+static int __init early_abort_handler(unsigned long addr, unsigned int fsr,
+				      struct pt_regs *regs)
+{
+	pr_warn("Hit pending imprecise external abort during first unmask, "
+		"this is most likely caused by a firmware/bootloader bug.\n");
+
+	return 0;
+}
+
+/*
  * Set up the device mappings.  Since we clear out the page tables for all
  * mappings above VMALLOC_START, except early fixmap, we might remove debug
  * device mappings.  This means earlycon can be used to debug this function
@@ -1269,7 +1284,7 @@ static void __init devicemaps_init(const struct machine_desc *mdesc)
 {
 	struct map_desc map;
 	unsigned long addr;
-	void *vectors;
+	void *vectors, *saved_fault_fn;
 
 	/*
 	 * Allocate the vector page early.
@@ -1365,7 +1380,9 @@ static void __init devicemaps_init(const struct machine_desc *mdesc)
 	flush_cache_all();
 
 	/* Enable asynchronous aborts */
+	saved_fault_fn = swap_fault_function(22, early_abort_handler);
 	local_abt_enable();
+	swap_fault_function(22, saved_fault_fn);
 }
 
 static void __init kmap_init(void)
-- 
2.6.1

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