From: Peter Zijlstra <peterz@infradead.org>
To: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Waiman Long <longman@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
"H. Peter Anvin" <hpa@zytor.com>,
Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
Jacob Pan <jacob.jun.pan@linux.intel.com>,
Len Brown <lenb@kernel.org>,
linux-kernel@vger.kernel.org, x86@kernel.org,
linux-pm@vger.kernel.org, Robin Jarry <rjarry@redhat.com>,
Joe Mario <jmario@redhat.com>
Subject: Re: [PATCH v3 2/3] intel_idle: Sync up the SPEC_CTRL MSR value to x86_spec_ctrl_current
Date: Thu, 22 Jun 2023 11:40:51 +0200 [thread overview]
Message-ID: <20230622094051.GF4253@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20230622054633.ulrurzzvzjijvdhn@treble>
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.
Arguably that's not even inconsistent because we disable/enable the
thing with IRQs disabled, so nothing can observe the difference.
next prev parent reply other threads:[~2023-06-22 9:51 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-22 0:36 [PATCH v3 0/3] x86/speculation: Disable IBRS when idle Waiman Long
2023-06-22 0:36 ` [PATCH v3 1/3] x86/idle: Disable IBRS when cpu is offline Waiman Long
2023-06-22 2:05 ` Randy Dunlap
2023-06-22 2:13 ` Waiman Long
2023-06-22 5:40 ` Josh Poimboeuf
2023-06-22 12:27 ` Waiman Long
2023-06-22 0:36 ` [PATCH v3 2/3] intel_idle: Sync up the SPEC_CTRL MSR value to x86_spec_ctrl_current Waiman Long
2023-06-22 5:46 ` Josh Poimboeuf
2023-06-22 9:38 ` Peter Zijlstra
2023-06-22 12:43 ` Waiman Long
2023-06-22 13:08 ` Peter Zijlstra
2023-06-22 9:40 ` Peter Zijlstra [this message]
2023-06-22 12:34 ` Waiman Long
2023-06-22 12:31 ` Waiman Long
2023-06-22 0:36 ` [PATCH v3 3/3] intel_idle: Add ibrs_off module parameter to force disable IBRS Waiman Long
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