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Message-ID: <7b8a5195-83c4-5433-6261-24e0941a1cab@redhat.com>
Date: Thu, 22 Jun 2023 08:31:57 -0400
From: Waiman Long <longman@...hat.com>
To: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>,
"H. Peter Anvin" <hpa@...or.com>,
Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
Jacob Pan <jacob.jun.pan@...ux.intel.com>,
Len Brown <lenb@...nel.org>, linux-kernel@...r.kernel.org,
x86@...nel.org, linux-pm@...r.kernel.org,
Robin Jarry <rjarry@...hat.com>, Joe Mario <jmario@...hat.com>
Subject: Re: [PATCH v3 2/3] intel_idle: Sync up the SPEC_CTRL MSR value to
x86_spec_ctrl_current
On 6/22/23 01:46, Josh Poimboeuf wrote:
> On Wed, Jun 21, 2023 at 08:36:02PM -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 which is at odd with the other code that
>> keep track of its state in that percpu variable. Fix that by updating
>> x86_spec_ctrl_current percpu value to always match the content of the
>> SPEC_CTRL MSR.
> Is this fixing an actual bug or is there some other reason for doing
> this?
It is not a bug per se. It is mainly to make the per cpu variable more
up to date.
>
>> Signed-off-by: Waiman Long <longman@...hat.com>
>> ---
>> 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);
>> + }
> More candidates for update_spec_ctrl()?
I don't think we can use update_spec_ctrl() here simply because of the
noinstr requirement. See commit 9b461a6faae7 ("cpuidle, intel_idle: Fix
CPUIDLE_FLAG_IBRS").
Cheers,
Longman
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