Messages in this thread | | | Date | Thu, 09 Jun 2022 12:20:10 +0100 | From | Marc Zyngier <> | Subject | Re: [PATCH] arm64: Clear OS lock in enable_debug_monitors |
| |
On Thu, 09 Jun 2022 04:33:18 +0100, Mark-PK Tsai <mark-pk.tsai@mediatek.com> wrote: > > Always clear OS lock before enable debug event. > > The OS lock is clear in cpuhp ops in recent kernel, > but when the debug exception happened before it > kernel might crash because debug event enable didn't > take effect when OS lock is hold. > > Below is the use case that having this problem: > > Register kprobe in console_unlock and kernel will > panic at secondary_start_kernel on secondary core.
Feels a bit extreme to do that, but hey...
> > CPU: 1 PID: 0 Comm: swapper/1 Tainted: P > ... > pstate: 004001c5 (nzcv dAIF +PAN -UAO) > pc : do_undefinstr+0x5c/0x60 > lr : do_undefinstr+0x2c/0x60 > sp : ffffffc01338bc50 > pmr_save: 000000f0 > x29: ffffffc01338bc50 x28: ffffff8115e95a00 T > x27: ffffffc01258e000 x26: ffffff8115e95a00 > x25: 00000000ffffffff x24: 0000000000000000 > x23: 00000000604001c5 x22: ffffffc014015008 > x21: 000000002232f000 x20: 00000000000000f0 j > x19: ffffffc01338bc70 x18: ffffffc0132ed040 > x17: ffffffc01258eb48 x16: 0000000000000403 L& > x15: 0000000000016480 x14: ffffffc01258e000 i/ > x13: 0000000000000006 x12: 0000000000006985 > x11: 00000000d5300000 x10: 0000000000000000 > x9 : 9f6c79217a8a0400 x8 : 00000000000000c5 > x7 : 0000000000000000 x6 : ffffffc01338bc08 2T > x5 : ffffffc01338bc08 x4 : 0000000000000002 > x3 : 0000000000000000 x2 : 0000000000000004 > x1 : 0000000000000000 x0 : 0000000000000001 *q > Call trace: > do_undefinstr+0x5c/0x60 > el1_undef+0x10/0xb4 > 0xffffffc014015008 > vprintk_func+0x210/0x290 > printk+0x64/0x90 > cpuinfo_detect_icache_policy+0x80/0xe0 > __cpuinfo_store_cpu+0x150/0x160 > secondary_start_kernel+0x154/0x440 > > The root cause is that OS_LSR_EL1.OSLK is reset > to 1 on a cold reset[1] and the firmware didn't > unlock it by default. > So the core didn't go to el1_dbg as expected after > kernel_enable_single_step and eret. > > [1] https://developer.arm.com/documentation/ddi0595/2021-06/AArch64-Registers/OSLSR-EL1--OS-Lock-Status-Register?lang=en > Signed-off-by: Mark-PK Tsai <mark-pk.tsai@mediatek.com> > --- > arch/arm64/kernel/debug-monitors.c | 23 ++++++++++++----------- > 1 file changed, 12 insertions(+), 11 deletions(-) > > diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c > index bf9fe71589bc..186f2846d652 100644 > --- a/arch/arm64/kernel/debug-monitors.c > +++ b/arch/arm64/kernel/debug-monitors.c > @@ -70,6 +70,17 @@ static int __init early_debug_disable(char *buf) > > early_param("nodebugmon", early_debug_disable); > > +/* > + * OS lock clearing. > + */ > +static int clear_os_lock(unsigned int cpu) > +{ > + write_sysreg(0, osdlr_el1); > + write_sysreg(0, oslar_el1); > + isb(); > + return 0; > +} > + > /* > * Keep track of debug users on each core. > * The ref counts are per-cpu so we use a local_t type. > @@ -91,6 +102,7 @@ void enable_debug_monitors(enum dbg_active_el el) > enable |= DBG_MDSCR_KDE; > > if (enable && debug_enabled) { > + clear_os_lock(0); > mdscr = mdscr_read(); > mdscr |= enable; > mdscr_write(mdscr); > @@ -119,17 +131,6 @@ void disable_debug_monitors(enum dbg_active_el el) > } > NOKPROBE_SYMBOL(disable_debug_monitors); > > -/* > - * OS lock clearing. > - */ > -static int clear_os_lock(unsigned int cpu) > -{ > - write_sysreg(0, osdlr_el1); > - write_sysreg(0, oslar_el1); > - isb(); > - return 0; > -} > - > static int __init debug_monitors_init(void) > { > return cpuhp_setup_state(CPUHP_AP_ARM64_DEBUG_MONITORS_STARTING,
If the OS Lock is cleared every time we enabled debug, what is the point of the notifier then?
Thanks,
M.
-- Without deviation from the norm, progress is not possible.
| |