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arm64: debug: clear mdscr_el1 instead of taking the OS lock 

During boot, we take the debug OS lock before interrupts are enabled.
This is required to prevent clearing of PSTATE.D on the interrupt entry
path, which could result in spurious debug exceptions before we've got
round to resetting things like the hardware breakpoints registers to a
sane state.

A problem with this approach is that taking the OS lock prevents an
external JTAG debugger from debugging the system, which is especially
irritating during boot, where JTAG debugging can be most useful.

This patch clears mdscr_el1 rather than taking the lock, clearing the
MDE and KDE bits and preventing self-hosted hardware debug exceptions
from occurring.

Tested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: stable@vger.kernel.org
This commit is contained in:
Will Deacon 2013-05-08 17:01:12 +01:00 committed by Catalin Marinas
parent 182a6f73ec
commit 9c413e25d9
2 changed files with 1 additions and 4 deletions
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2
arch/arm64/kernel/debug-monitors.c
View File

@ -136,8 +136,6 @@ void disable_debug_monitors(enum debug_el el)
*/
static void clear_os_lock(void *unused)
{
asm volatile("msr mdscr_el1, %0" : : "r" (0));
isb();
asm volatile("msr oslar_el1, %0" : : "r" (0));
isb();
}

3
arch/arm64/mm/proc.S
View File

@ -119,8 +119,7 @@ ENTRY(__cpu_setup)
mov x0, #3 << 20
msr cpacr_el1, x0 // Enable FP/ASIMD
mov x0, #1
msr oslar_el1, x0 // Set the debug OS lock
msr mdscr_el1, xzr // Reset mdscr_el1
tlbi vmalle1is // invalidate I + D TLBs
/*
* Memory region attributes for LPAE: