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

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Date:   Fri, 11 Nov 2016 12:54:46 -0800
From:   Nadav Amit <nadav.amit@...il.com>
To:     Kyle Huey <me@...ehuey.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>,
        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 <kvm@...r.kernel.org>
Subject: Re: [PATCH v11 7/7] KVM: x86: virtualize cpuid faulting


> 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).

Nadav