linux-kernel - Re: [PATCH v14 0/9] x86/arch_prctl Add ARCH_[GET|SET]_CPUID for controlling the CPUID instruction

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Date:   Fri, 10 Feb 2017 14:07:03 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Kyle Huey <me@...ehuey.com>
cc:     Robert O'Callahan <robert@...llahan.org>,
        Andy Lutomirski <luto@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Jeff Dike <jdike@...toit.com>,
        Richard Weinberger <richard@....at>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Shuah Khan <shuah@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Borislav Petkov <bp@...e.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Len Brown <len.brown@...el.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Dmitry Safonov <dsafonov@...tuozzo.com>,
        David Matlack <dmatlack@...gle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
        user-mode-linux-devel@...ts.sourceforge.net,
        user-mode-linux-user@...ts.sourceforge.net,
        linux-fsdevel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH v14 0/9] x86/arch_prctl Add ARCH_[GET|SET]_CPUID for
 controlling the CPUID instruction

On Wed, 8 Feb 2017, Kyle Huey wrote:

> rr (http://rr-project.org/), a userspace record-and-replay reverse-
> execution debugger, would like to trap and emulate the CPUID instruction.
> This would allow us to a) mask away certain hardware features that rr does
> not support (e.g. RDRAND) and b) enable trace portability across machines
> by providing constant results.
> 
> Newer Intel CPUs (Ivy Bridge and later) can fault when CPUID is executed at
> CPL > 0. Expose this capability to userspace as a new pair of arch_prctls,
> ARCH_GET_CPUID and ARCH_SET_CPUID.
> 
> Since v13:
> All: rebased on top of tglx's __switch_to_xtra patches
> (https://lkml.org/lkml/2016/12/15/432)

That doesn't help because that patchset is stale and it has unresolved
comments. I don't know when I have cycles to revisit it, but if you want to
have a try feel free to do so.

Thanks,

	tglx