linux-kernel - [PATCH v2] intel_idle: avoid tracing MSR writes while idling

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Message-Id: <20220824234211.1625026-1-pshier@google.com>
Date:   Wed, 24 Aug 2022 16:42:11 -0700
From:   Peter Shier <pshier@...gle.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Len Brown <lenb@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Michael Roth <michael.roth@....com>,
        Alexei Starovoitov <ast@...nel.org>,
        Josh Poimboeuf <jpoimboe@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        Peter Shier <pshier@...gle.com>
Subject: [PATCH v2] intel_idle: avoid tracing MSR writes while idling

With commit bf5835bcdb963 ("intel_idle: Disable IBRS during long idle"),
enabling wrmsr trace with CONFIG_LOCKDEP causes "suspicious
rcu_dereference_check() usage" warning because do_trace_write_msr does not
use trace_write_msr_rcuidle.

Change intel_idle_ibrs to use native_wrmsr to avoid tracing

Sample warning:
============================
WARNING: suspicious RCU usage
6.0.0-dbg-DEV #7 Tainted: G S         O
-----------------------------
arch/x86/include/asm/msr-trace.h:48 suspicious rcu_dereference_check() usage!

other info that might help us debug this:

rcu_scheduler_active = 2, debug_locks = 1
RCU used illegally from extended quiescent state!
no locks held by swapper/59/0.

stack backtrace:
CPU: 59 PID: 0 Comm: swapper/59 Tainted: G S         O       6.0.0-dbg-DEV #7
Call Trace:
 dump_stack_lvl
 dump_stack
 lockdep_rcu_suspicious
 trace_write_msr
 do_trace_write_msr
 intel_idle_ibrs
 cpuidle_enter_state
 cpuidle_enter
 do_idle
 cpu_startup_entry
 start_secondary
 secondary_startup_64_no_verify

Tested on skylake using:
echo "msr:write_msr" >/sys/kernel/debug/tracing/set_event
with and without patch.

Signed-off-by: Peter Shier <pshier@...gle.com>
---

v2:
- changed to avoid tracing

v1: https://lore.kernel.org/all/20220823234353.937002-1-pshier@google.com/

 drivers/idle/intel_idle.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c
index 3e101719689a..df129c73786f 100644
--- a/drivers/idle/intel_idle.c
+++ b/drivers/idle/intel_idle.c
@@ -187,12 +187,12 @@ static __cpuidle int intel_idle_ibrs(struct cpuidle_device *dev,
 	int ret;
 
 	if (smt_active)
-		wrmsrl(MSR_IA32_SPEC_CTRL, 0);
+		native_wrmsr(MSR_IA32_SPEC_CTRL, 0);
 
 	ret = __intel_idle(dev, drv, index);
 
 	if (smt_active)
-		wrmsrl(MSR_IA32_SPEC_CTRL, spec_ctrl);
+		native_wrmsr(MSR_IA32_SPEC_CTRL, spec_ctrl);
 
 	return ret;
 }
--