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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Steven Noonan <steven@uplinklabs.net>
Cc:     Muhammad Usama Anjum <usama.anjum@collabora.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>,
        "Guilherme G. Piccoli" <gpiccoli@igalia.com>, kernel@collabora.com
Subject: Re: Direct rdtsc call side-effect
In-Reply-To: <871qivdjui.ffs@tglx>
References: <6719fb05-382c-8ec4-ccda-72798906a54b@collabora.com>
 <87mt1jeax1.ffs@tglx> <87h6rrdoy0.ffs@tglx>
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 <871qivdjui.ffs@tglx>
Date:   Thu, 01 Jun 2023 22:13:29 +0200
Message-ID: <87y1l3c55i.ffs@tglx>
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On Thu, Jun 01 2023 at 22:10, Thomas Gleixner wrote:
>
> So back to the options:
>
>    1) Kernel
>
>       If at all then this needs to be disabled by default and enabled by
>       a command line option along with a big fat warning that it might
>       disable TSC for timekeeping and bug reports related to this are
>       going to be ignored.
>
>       Honestly I'm not too interested in this. It's yet another piece of
>       art which needs to be maintained and kept alive for a long time.
>
>       The fact that we need to check for synchronized TSCs in the first
>       place is hillarious already. TSC_ADJUST makes the resynchronization
>       attempt at least halfways sensible.
>
>       Without it, it's just a pile of never going to be correct
>       heuristics with a flood of "this fixes it for my machine (and
>       breaks the rest)" patches.
>
>
>    2) Binary patching
>
>       Unfortunately RDTSC is only a two byte instruction, but there are
>       enough advanced binary patching tools to deal with that.
>
>       It might be a completely crazy idea, but I wouldn't dismiss it
>       before trying.

Duh. Hit send too early

     3) Virtualization

        Obviously not trivial either but definitely workable.

Thanks,

        tglx