linux-kernel - Re: [PATCH v2 5/5] x86/idle: Disable IBRS entering mwait idle and enable it on wakeup

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <dcc515cd-d0cf-5a14-8b48-aa94770e50bd@redhat.com>
Date:   Wed, 21 Jun 2023 10:05:06 -0400
From:   Waiman Long <longman@...hat.com>
To:     Peter Zijlstra <peterz@...radead.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>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        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 v2 5/5] x86/idle: Disable IBRS entering mwait idle and
 enable it on wakeup

On 6/21/23 03:32, Peter Zijlstra wrote:
> On Tue, Jun 20, 2023 at 10:06:25AM -0400, Waiman Long wrote:
>> When a user sets "intel_idle.max_cstate=0", it will disable
>> intel_idle and fall back to acpi_idle instead. The acpi_idle code
>> will then call mwait_idle_with_hints() to enter idle state. So when
>> X86_FEATURE_KERNEL_IBRS is enabled, it is necessary to disable IBRS
>> within mwait_idle_with_hints() when IRQ was disabled to avoid performance
>> degradation on silbing thread running user workload.
> Urgh, no, just no. This is nasty.

OK, will take this out in the next version.

Cheers,
Longman