From: Will Deacon will@kernel.org
commit a2c42bbabbe260b7626d8459093631a6e16ee0ee upstream.
The Spectre-v4 workaround is re-configured when resuming from suspend, as the firmware may have re-enabled the mitigation despite the user previously asking for it to be disabled.
Enabling or disabling the workaround can result in an undefined instruction exception on CPUs which implement PSTATE.SSBS but only allow it to be configured by adjusting the SPSR on exception return. We handle this by installing an 'undef hook' which effectively emulates the access.
Installing this hook requires us to take a couple of spinlocks both to avoid corrupting the internal list of hooks but also to ensure that we don't run into an unhandled exception. Unfortunately, when resuming from suspend, we haven't yet called rcu_idle_exit() and so lockdep gets angry about "suspicious RCU usage". In doing so, it tries to print a warning, which leads it to get even more suspicious, this time about itself:
| rcu_scheduler_active = 2, debug_locks = 1 | RCU used illegally from extended quiescent state! | 1 lock held by swapper/0: | #0: (logbuf_lock){-.-.}-{2:2}, at: vprintk_emit+0x88/0x198 | | Call trace: | dump_backtrace+0x0/0x1d8 | show_stack+0x18/0x24 | dump_stack+0xe0/0x17c | lockdep_rcu_suspicious+0x11c/0x134 | trace_lock_release+0xa0/0x160 | lock_release+0x3c/0x290 | _raw_spin_unlock+0x44/0x80 | vprintk_emit+0xbc/0x198 | vprintk_default+0x44/0x6c | vprintk_func+0x1f4/0x1fc | printk+0x54/0x7c | lockdep_rcu_suspicious+0x30/0x134 | trace_lock_acquire+0xa0/0x188 | lock_acquire+0x50/0x2fc | _raw_spin_lock+0x68/0x80 | spectre_v4_enable_mitigation+0xa8/0x30c | __cpu_suspend_exit+0xd4/0x1a8 | cpu_suspend+0xa0/0x104 | psci_cpu_suspend_enter+0x3c/0x5c | psci_enter_idle_state+0x44/0x74 | cpuidle_enter_state+0x148/0x2f8 | cpuidle_enter+0x38/0x50 | do_idle+0x1f0/0x2b4
Prevent these splats by running __cpu_suspend_exit() with RCU watching.
Cc: Mark Rutland mark.rutland@arm.com Cc: Lorenzo Pieralisi lorenzo.pieralisi@arm.com Cc: Peter Zijlstra peterz@infradead.org Cc: Boqun Feng boqun.feng@gmail.com Cc: Marc Zyngier maz@kernel.org Cc: Saravana Kannan saravanak@google.com Suggested-by: "Paul E . McKenney" paulmck@kernel.org Reported-by: Sami Tolvanen samitolvanen@google.com Fixes: c28762070ca6 ("arm64: Rewrite Spectre-v4 mitigation code") Cc: stable@vger.kernel.org Acked-by: Paul E. McKenney paulmck@kernel.org Acked-by: Marc Zyngier maz@kernel.org Acked-by: Mark Rutland mark.rutland@arm.com Link: https://lore.kernel.org/r/20210218140346.5224-1-will@kernel.org Signed-off-by: Will Deacon will@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/arm64/kernel/suspend.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/arch/arm64/kernel/suspend.c +++ b/arch/arm64/kernel/suspend.c @@ -120,7 +120,7 @@ int cpu_suspend(unsigned long arg, int ( if (!ret) ret = -EOPNOTSUPP; } else { - __cpu_suspend_exit(); + RCU_NONIDLE(__cpu_suspend_exit()); }
unpause_graph_tracing();