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Message-ID: <87c6e059-d010-a8aa-8e63-7b09d82be863@redhat.com>
Date: Thu, 22 Jun 2023 08:34:59 -0400
From: Waiman Long <longman@...hat.com>
To: Peter Zijlstra <peterz@...radead.org>,
Josh Poimboeuf <jpoimboe@...nel.org>
Cc: 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 05:40, Peter Zijlstra wrote:
> On Wed, Jun 21, 2023 at 10:46:33PM -0700, 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?
> No actual bug, he did this for his debugfs file -- which is no longer
> part of the series. With that on, you can observe the
> x86_spec_ctrl_current value while idle.
Right. That is the main reason as I want the SPEC_CTRL MSRs value to be
observable by some external mean:-)
Regards,
Longman
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