2023-06-20 14:40:30

by Waiman Long

Subject: [PATCH v2 3/5] intel_idle: Sync up the SPEC_CTRL MSR value to x86_spec_ctrl_current

When intel_idle_ibrs() is called, it modifies the SPEC_CTRL MSR to 0
in order disable IBRS. However, the new MSR value isn't reflected in
x86_spec_ctrl_current. That will cause the new spec_ctrl_msrs debugfs
file to show incorrect result. Fix that by updating x86_spec_ctrl_current
percpu value to always match the content of the SPEC_CTRL MSR.

Signed-off-by: Waiman Long <[email protected]>
---
drivers/idle/intel_idle.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c
index aa2d19db2b1d..07fa23707b3c 100644
--- a/drivers/idle/intel_idle.c
+++ b/drivers/idle/intel_idle.c
@@ -181,13 +181,17 @@ static __cpuidle int intel_idle_ibrs(struct cpuidle_device *dev,
u64 spec_ctrl = spec_ctrl_current();
int ret;

- if (smt_active)
+ if (smt_active) {
+ __this_cpu_write(x86_spec_ctrl_current, 0);
native_wrmsrl(MSR_IA32_SPEC_CTRL, 0);
+ }

ret = __intel_idle(dev, drv, index);

- if (smt_active)
+ if (smt_active) {
native_wrmsrl(MSR_IA32_SPEC_CTRL, spec_ctrl);
+ __this_cpu_write(x86_spec_ctrl_current, spec_ctrl);
+ }

return ret;
}
--
2.31.1

2023-06-21 08:31:21

by Peter Zijlstra

Subject: Re: [PATCH v2 3/5] intel_idle: Sync up the SPEC_CTRL MSR value to x86_spec_ctrl_current

On Tue, Jun 20, 2023 at 10:06:23AM -0400, Waiman Long wrote:
> When intel_idle_ibrs() is called, it modifies the SPEC_CTRL MSR to 0
> in order disable IBRS. However, the new MSR value isn't reflected in
> x86_spec_ctrl_current. That will cause the new spec_ctrl_msrs debugfs
> file to show incorrect result. Fix that by updating x86_spec_ctrl_current
> percpu value to always match the content of the SPEC_CTRL MSR.

What debugfs file?