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Subject[PATCH] x86: handle MSR exception when setting energy perf bias
Date
On very rare occasions, immediately after a suspend, one of our
SandyBridge CI boxes hits the exception below on CPU0 while trying to
reconfigure the energy bias register. As far as I can tell, this is not
likely a race in the kernel, since we have only one cpu online, no
preempt and irqs_disabled, and it can only be reproduced in this
specific SNB-2600 on rare occasions. It looks more of a faulty hardware
thing to me.

Still, we can handle this exception more gracefully to silence the CI,
by using the safe version of the msrl_read/write wrapper.

The log on the faulty box is as follows:

[ 280.969486] unchecked MSR access error: RDMSR from 0x1b0 at rIP: 0xffffffff81030a4f (init_intel_energy_perf.part.3+0xf/0xb0)
[ 280.969488] Call Trace:
[ 280.969492] intel_bsp_resume+0x1a/0x20
[ 280.969494] bsp_resume+0x1d/0x20
[ 280.969498] syscore_resume+0x62/0x320
[ 280.969501] suspend_devices_and_enter+0xa09/0xcd0
[ 280.969506] pm_suspend+0x574/0xa00
[ 280.969509] state_store+0x82/0xf0
[ 280.969514] kobj_attr_store+0xf/0x20
[ 280.969516] sysfs_kf_write+0x45/0x60
[ 280.969519] kernfs_fop_write+0x124/0x1c0
[ 280.969524] __vfs_write+0x28/0x130
[ 280.969526] ? rcu_read_lock_sched_held+0x7a/0x90
[ 280.969528] ? rcu_sync_lockdep_assert+0x2f/0x60
[ 280.969531] ? __sb_start_write+0x10c/0x200
[ 280.969535] vfs_write+0xc8/0x1c0
[ 280.969538] SyS_write+0x49/0xb0
[ 280.969542] entry_SYSCALL_64_fastpath+0x1c/0xb1
[ 280.969544] RIP: 0033:0x7fb6721ce8f0
[ 280.969546] RSP: 002b:00007ffc3ac05da8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
[ 280.969549] RAX: ffffffffffffffda RBX: ffffffff81489d83 RCX: 00007fb6721ce8f0
[ 280.969551] RDX: 0000000000000004 RSI: 00005634312da060 RDI: 0000000000000007
[ 280.969552] RBP: ffffc90001147f88 R08: 00005634312d7de0 R09: 00007fb67269f700
[ 280.969554] R10: 00007fb672497b58 R11: 0000000000000246 R12: 00005634312d7d00
[ 280.969555] R13: 0000000000000001 R14: 0000000000000004 R15: 0000000000000004
[ 280.969559] ? __this_cpu_preempt_check+0x13/0x20
[ 280.969566] unchecked MSR access error: WRMSR to 0x1b0 (tried to write 0x0000000000000006) at rIP: 0xffffffff81030a8e (init_intel_energy_perf.part.3+0x4e/0xb0)
[ 280.969567] Call Trace:
[ 280.969569] intel_bsp_resume+0x1a/0x20
[ 280.969571] bsp_resume+0x1d/0x20
[ 280.969573] syscore_resume+0x62/0x320
[ 280.969576] suspend_devices_and_enter+0xa09/0xcd0
[ 280.969580] pm_suspend+0x574/0xa00
[ 280.969584] state_store+0x82/0xf0
[ 280.969587] kobj_attr_store+0xf/0x20
[ 280.969589] sysfs_kf_write+0x45/0x60
[ 280.969592] kernfs_fop_write+0x124/0x1c0
[ 280.969595] __vfs_write+0x28/0x130
[ 280.969597] ? rcu_read_lock_sched_held+0x7a/0x90
[ 280.969599] ? rcu_sync_lockdep_assert+0x2f/0x60
[ 280.969601] ? __sb_start_write+0x10c/0x200
[ 280.969605] vfs_write+0xc8/0x1c0
[ 280.969608] SyS_write+0x49/0xb0
[ 280.969612] entry_SYSCALL_64_fastpath+0x1c/0xb1
[ 280.969613] RIP: 0033:0x7fb6721ce8f0
[ 280.969614] RSP: 002b:00007ffc3ac05da8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
[ 280.969617] RAX: ffffffffffffffda RBX: ffffffff81489d83 RCX: 00007fb6721ce8f0
[ 280.969619] RDX: 0000000000000004 RSI: 00005634312da060 RDI: 0000000000000007
[ 280.969620] RBP: ffffc90001147f88 R08: 00005634312d7de0 R09: 00007fb67269f700
[ 280.969621] R10: 00007fb672497b58 R11: 0000000000000246 R12: 00005634312d7d00
[ 280.969623] R13: 0000000000000001 R14: 0000000000000004 R15: 0000000000000004
[ 280.969626] ? __this_cpu_preempt_check+0x13/0x20

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=102365
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.co.uk>
---
arch/x86/kernel/cpu/intel.c | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index dfa90a3a5145..51082a9a3d8a 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -465,14 +465,17 @@ static void init_intel_energy_perf(struct cpuinfo_x86 *c)
if (!cpu_has(c, X86_FEATURE_EPB))
return;

- rdmsrl(MSR_IA32_ENERGY_PERF_BIAS, epb);
- if ((epb & 0xF) != ENERGY_PERF_BIAS_PERFORMANCE)
+ if (rdmsrl_safe(MSR_IA32_ENERGY_PERF_BIAS, &epb) ||
+ (epb & 0xF) != ENERGY_PERF_BIAS_PERFORMANCE)
return;

+ epb = (epb & ~0xF) | ENERGY_PERF_BIAS_NORMAL;
+ if (wrmsrl_safe(MSR_IA32_ENERGY_PERF_BIAS, epb)) {
+ pr_warn_once("ENERGY_PERF_BIAS: Failed to set to 'normal'\n");
+ return;
+ }
pr_warn_once("ENERGY_PERF_BIAS: Set to 'normal', was 'performance'\n");
pr_warn_once("ENERGY_PERF_BIAS: View and update with x86_energy_perf_policy(8)\n");
- epb = (epb & ~0xF) | ENERGY_PERF_BIAS_NORMAL;
- wrmsrl(MSR_IA32_ENERGY_PERF_BIAS, epb);
}

static void intel_bsp_resume(struct cpuinfo_x86 *c)
--
2.11.0
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