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From: Kyle Huey <me@kylehuey.com>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	John Stultz <john.stultz@linaro.org>,
	Ingo Molnar <mingo@redhat.com>, Michal Hocko <mhocko@suse.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Aravind Gopalakrishnan <Aravind.Gopalakrishnan@amd.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	"Luis R. Rodriguez" <mcgrof@kernel.org>,
	Mateusz Guzik <mguzik@redhat.com>,
	Alex Thorlton <athorlton@sgi.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
	Dmitry Vyukov <dvyukov@google.com>,
	Vladimir Zapolskiy <vladimir_zapolskiy@mentor.com>,
	Jiri Slaby <jslaby@suse.cz>,
	Andrey Ryabinin <aryabinin@virtuozzo.com>,
	Ben Segall <bsegall@google.com>,
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
	<x86@kernel.org>, Denys Vlasenko <dvlasenk@redhat.com>,
	Paul Gortmaker <paul.gortmaker@windriver.com>,
	Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
	"Robert O'Callahan" <robert@ocallahan.org>,
	"open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
	<linux-kernel@vger.kernel.org>, Juergen Gross <jgross@suse.com>,
	Linux API <linux-api@vger.kernel.org>,
	Fenghua Yu <fenghua.yu@intel.com>,
	Kees Cook <keescook@chromium.org>,
	"Peter Zijlstra (Intel)" <peterz@infradead.org>,
	Borislav Petkov <bp@suse.de>, Len Brown <len.brown@intel.com>,
	Huang Rui <ray.huang@amd.com>, "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH] prctl,x86 Add PR_[GET|SET]_CPUID for controlling the CPUID instruction.
Date: Tue, 13 Sep 2016 23:13:40 -0700	[thread overview]
Message-ID: <CAP045ApLcQXZP44wry8mofLz2ip1vQbvpnhCjQZsT+JxXmVEzg@mail.gmail.com> (raw)
In-Reply-To: <CALCETrVJAib918qn9CL4Tvyfok-8eAHimYDabXUF=1Nsxo4-Pw@mail.gmail.com>

On Mon, Sep 12, 2016 at 9:56 AM, Andy Lutomirski <luto@amacapital.net> wrote:
> You should explicitly check that, if the
> feature is set under Xen PV, then the MSR actually works as
> advertised.  This may require talking to the Xen folks to make sure
> you're testing the right configuration.

This is interesting.  When running under Xen PV the kernel is allowed
to read the real value of MSR_PLATFORM_INFO and see that CPUID
faulting is supported.  But as you suggested, writing to
MSR_MISC_FEATURES_ENABLES doesn't actually enable CPUID faulting, at
least not in any way that works.

It's not obvious to me how to test this, because when this feature
works, CPUID only faults in userspace, not in the kernel.  Is there
existing code somewhere that runs tests like this in userspace?

- Kyle

WARNING: multiple messages have this Message-ID (diff)
From: Kyle Huey <me-OhBmq/TcCDJWk0Htik3J/w@public.gmane.org>
To: Andy Lutomirski <luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org>
Cc: Thomas Gleixner <tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>,
	John Stultz <john.stultz-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>,
	Ingo Molnar <mingo-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
	Michal Hocko <mhocko-IBi9RG/b67k@public.gmane.org>,
	Andrew Morton
	<akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>,
	"Michael S. Tsirkin"
	<mst-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
	Alexander Shishkin
	<alexander.shishkin-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>,
	Aravind Gopalakrishnan
	<Aravind.Gopalakrishnan-5C7GfCeVMHo@public.gmane.org>,
	Vlastimil Babka <vbabka-AlSwsSmVLrQ@public.gmane.org>,
	"Luis R. Rodriguez"
	<mcgrof-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	Mateusz Guzik <mguzik-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
	Alex Thorlton <athorlton-sJ/iWh9BUns@public.gmane.org>,
	"Rafael J. Wysocki"
	<rafael.j.wysocki-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>,
	Dmitry Vyukov <dvyukov-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>,
	Vladimir Zapolskiy
	<vladimir_zapolskiy-nmGgyN9QBj3QT0dZR+AlfA@public.gmane.org>,
	Jiri Slaby <jslaby-AlSwsSmVLrQ@public.gmane.org>,
	Andrey Ryabinin
	<aryabinin-5HdwGun5lf+gSpxsJD1C4w@public.gmane.org>,
	Ben Segall <bsegall-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>,
	maintainer:X86 ARCHITECTURE (32-BIT
Subject: Re: [PATCH] prctl,x86 Add PR_[GET|SET]_CPUID for controlling the CPUID instruction.
Date: Tue, 13 Sep 2016 23:13:40 -0700	[thread overview]
Message-ID: <CAP045ApLcQXZP44wry8mofLz2ip1vQbvpnhCjQZsT+JxXmVEzg@mail.gmail.com> (raw)
In-Reply-To: <CALCETrVJAib918qn9CL4Tvyfok-8eAHimYDabXUF=1Nsxo4-Pw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>

On Mon, Sep 12, 2016 at 9:56 AM, Andy Lutomirski <luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org> wrote:
> You should explicitly check that, if the
> feature is set under Xen PV, then the MSR actually works as
> advertised.  This may require talking to the Xen folks to make sure
> you're testing the right configuration.

This is interesting.  When running under Xen PV the kernel is allowed
to read the real value of MSR_PLATFORM_INFO and see that CPUID
faulting is supported.  But as you suggested, writing to
MSR_MISC_FEATURES_ENABLES doesn't actually enable CPUID faulting, at
least not in any way that works.

It's not obvious to me how to test this, because when this feature
works, CPUID only faults in userspace, not in the kernel.  Is there
existing code somewhere that runs tests like this in userspace?

- Kyle

  parent reply	other threads:[~2016-09-14  6:13 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-09-12  0:29 [PATCH] prctl,x86 Add PR_[GET|SET]_CPUID for controlling the CPUID instruction Kyle Huey
2016-09-12  0:29 ` Kyle Huey
2016-09-12  9:07 ` Borislav Petkov
2016-09-12  9:07   ` Borislav Petkov
2016-09-12 14:15   ` Kyle Huey
2016-09-12 14:15     ` Kyle Huey
2016-09-12 14:34     ` Borislav Petkov
2016-09-12 14:34       ` Borislav Petkov
2016-09-12 14:34       ` Borislav Petkov
2016-09-13 18:42     ` Kyle Huey
2016-09-13 18:42       ` Kyle Huey
2016-09-12 16:56 ` Andy Lutomirski
2016-09-12 16:56   ` Andy Lutomirski
2016-09-12 17:18   ` Borislav Petkov
2016-09-12 17:18     ` Borislav Petkov
2016-09-12 17:56   ` Jann Horn
2016-09-12 17:56     ` Jann Horn
2016-09-12 21:07     ` Andy Lutomirski
2016-09-12 21:07       ` Andy Lutomirski
2016-09-14  6:13   ` Kyle Huey [this message]
2016-09-14  6:13     ` Kyle Huey
2016-09-14 18:52     ` Andy Lutomirski
2016-09-14 18:52       ` Andy Lutomirski
2016-09-14 19:22       ` Andrew Cooper
2016-09-14 19:22         ` Andrew Cooper
2016-09-14 19:23       ` Boris Ostrovsky
2016-09-14 19:23         ` Boris Ostrovsky
2016-09-14 19:28         ` Andrew Cooper
2016-09-14 19:28           ` Andrew Cooper
2016-09-14 19:36           ` Andy Lutomirski
2016-09-14 19:36             ` Andy Lutomirski
2016-09-14 19:42             ` Andrew Cooper
2016-09-14 19:42               ` Andrew Cooper
2016-09-14 19:42             ` [PATCH] prctl, x86 " Andrew Cooper
2016-09-12 17:37 ` [PATCH] prctl,x86 " Andi Kleen
2016-09-12 18:25   ` Henrique de Moraes Holschuh

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