linux-kernel - Re: [PATCH v7 0/6] x86/arch_prctl Add ARCH_[GET|SET]_CPUID for controlling the CPUID instruction

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Date:   Mon, 24 Oct 2016 22:30:58 -0700
From:   Kyle Huey <me@...ehuey.com>
To:     "Robert O'Callahan" <robert@...llahan.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Jeff Dike <jdike@...toit.com>,
        Richard Weinberger <richard@....at>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...e.de>,
        Dmitry Safonov <dsafonov@...tuozzo.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Shuah Khan <shuah@...nel.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Len Brown <len.brown@...el.com>
Cc:     open list <linux-kernel@...r.kernel.org>,
        "open list:USER-MODE LINUX (UML)" 
        <user-mode-linux-devel@...ts.sourceforge.net>,
        "open list:USER-MODE LINUX (UML)" 
        <user-mode-linux-user@...ts.sourceforge.net>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH v7 0/6] x86/arch_prctl Add ARCH_[GET|SET]_CPUID for
 controlling the CPUID instruction

On Tue, Oct 18, 2016 at 7:03 PM, Kyle Huey <me@...ehuey.com> 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, with two values, ARCH_CPUID_ENABLE and
> ARCH_CPUID_SIGSEGV.
>
> v6 did not get any feedback, so I included the changes since v5.
>
> Since v6:
> - Rebased to 4.9-rc1 (primarily over the new VDSO arch_prctls and the new pkey
>   entries in the syscall table)
>
> Since v5:
>
> Patch 3:
> - do_arch_prctl is again do_arch_prctl_common
>
> Patch 6:
> - Added static qualifiers on get/set_cpuid_mode
> - Braced ifs in disable/enable_cpuid
> - Renamed arch_post_exec to arch_setup_new_exec
>

A friendly ping.  Has anybody had an opportunity to look at this patch
series again?  Any feedback, positive or negative, would be greatly
appreciated.

- Kyle