ARM: hw_breakpoint: disable preemption during debug exception handling
On ARM, debug exceptions occur in the form of data or prefetch aborts.
One difference is that debug exceptions require access to per-cpu banked
registers and data structures which are not saved in the low-level exception
code. For kernels built with CONFIG_PREEMPT, there is an unlikely scenario
that the debug handler ends up running on a different CPU from the one
that originally signalled the event, resulting in random data being read
from the wrong registers.
This patch adds a debug_entry macro to the low-level exception handling
code which checks whether the taken exception is a debug exception. If
it is, the preempt count for the faulting process is incremented. After
the debug handler has finished, the count is decremented.
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index c09e357..34bbef0 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -198,6 +198,7 @@
@
@ set desired IRQ state, then call main handler
@
+ debug_entry r1
msr cpsr_c, r9
mov r2, sp
bl do_DataAbort
@@ -324,6 +325,7 @@
#else
bl CPU_PABORT_HANDLER
#endif
+ debug_entry r1
msr cpsr_c, r9 @ Maybe enable interrupts
mov r2, sp @ regs
bl do_PrefetchAbort @ call abort handler
@@ -439,6 +441,7 @@
@
@ IRQs on, then call the main handler
@
+ debug_entry r1
enable_irq
mov r2, sp
adr lr, BSYM(ret_from_exception)
@@ -703,6 +706,7 @@
#else
bl CPU_PABORT_HANDLER
#endif
+ debug_entry r1
enable_irq @ Enable interrupts
mov r2, sp @ regs
bl do_PrefetchAbort @ call abort handler