linux-kernel - Re: [PATCH v4 2/5] x86/umwait: Initialize umwait control values

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: <CALCETrWtmrwqjThkMKU9YpTDK4o95V4HBb2_yQF2tvx5JZ9Ukw@mail.gmail.com>
Date:   Sat, 8 Jun 2019 15:52:42 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Fenghua Yu <fenghua.yu@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        H Peter Anvin <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Ashok Raj <ashok.raj@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [PATCH v4 2/5] x86/umwait: Initialize umwait control values

On Fri, Jun 7, 2019 at 3:10 PM Fenghua Yu <fenghua.yu@...el.com> wrote:
>
> umwait or tpause allows processor to enter a light-weight
> power/performance optimized state (C0.1 state) or an improved
> power/performance optimized state (C0.2 state) for a period
> specified by the instruction or until the system time limit or until
> a store to the monitored address range in umwait.
>
> IA32_UMWAIT_CONTROL MSR register allows kernel to enable/disable C0.2
> on the processor and set maximum time the processor can reside in
> C0.1 or C0.2.
>
> By default C0.2 is enabled so the user wait instructions can enter the
> C0.2 state to save more power with slower wakeup time.

Sounds good, but:

> +#define MSR_IA32_UMWAIT_CONTROL_C02            BIT(0)

> +static u32 umwait_control_cached = 100000;

The code seems to disagree.