From mboxrd@z Thu Jan  1 00:00:00 1970
From: Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH v14 0/9] x86/arch_prctl Add ARCH_[GET|SET]_CPUID for
 controlling the CPUID instruction
Date: Fri, 10 Feb 2017 14:07:03 +0100 (CET)
Message-ID: <alpine.DEB.2.20.1702101405570.4036@nanos>
References: <20170208080917.24320-1-khuey@kylehuey.com>
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Cc: Robert O'Callahan <robert@ocallahan.org>,
        Andy Lutomirski <luto@kernel.org>,
        Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, x86@kernel.org,
        Paolo Bonzini <pbonzini@redhat.com>,
        =?ISO-8859-2?Q?Radim_Kr=E8m=E1=F8?= <rkrcmar@redhat.com>,
        Jeff Dike <jdike@addtoit.com>,
        Richard Weinberger <richard@nod.at>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Shuah Khan <shuah@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Borislav Petkov <bp@suse.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Len Brown <len.brown@intel.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
        Dmitry Safonov <dsafonov@virtuozzo.com>,
        David Matlack <dmatlack@google.com>,
        Nadav Amit <nadav.amit@gmail.com>,
To: Kyle Huey <me@kylehuey.com>
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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