linux-kernel - Re: [PATCH v11 7/7] KVM: x86: virtualize cpuid faulting

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Message-ID: <CAP045AqG5f5pJLYVVnFZfrFv8h8ZzpcD=bkS+tJrVWE_vX48Qg@mail.gmail.com>
Date:   Wed, 16 Nov 2016 08:40:09 -0800
From:   Kyle Huey <me@...ehuey.com>
To:     Nadav Amit <nadav.amit@...il.com>
Cc:     "Robert O'Callahan" <robert@...llahan.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, X86 ML <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>,
        LKML <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:FILESYSTEMS (VFS and infrastructure)" 
        <linux-fsdevel@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH v11 7/7] KVM: x86: virtualize cpuid faulting

On Fri, Nov 11, 2016 at 12:54 PM, Nadav Amit <nadav.amit@...il.com> wrote:
>
>> On Nov 10, 2016, at 3:40 PM, Kyle Huey <me@...ehuey.com> wrote:
>>
>> Hardware support for faulting on the cpuid instruction is not required to
>> emulate it, because cpuid triggers a VM exit anyways. KVM handles the relevant
>> MSRs (MSR_PLATFORM_INFO and MSR_MISC_FEATURES_ENABLE) and upon a
>> cpuid-induced VM exit checks the cpuid faulting state and the CPL.
>> kvm_require_cpl is even kind enough to inject the GP fault for us.
>
> I think that for consistency you should also revise em_cpuid() of KVM
> instruction emulator. Otherwise it may be a potential security
> hazard (as far fetched as it currently seems).

Hmm, ok.  Do you know how I can test this code path?

- Kyle