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From:   Jim Mattson <jmattson@google.com>
Date:   Wed, 31 Jan 2018 12:54:08 -0800
Message-ID: <CALMp9eT677DU=EGoezcyjRMAP3XKiK_6FBJb-rVQrBX2CSbTuw@mail.gmail.com>
Subject: Re: [PATCH v5 4/5] KVM: VMX: Allow direct access to MSR_IA32_SPEC_CTRL
To:     Paolo Bonzini <pbonzini@redhat.com>
Cc:     KarimAllah Ahmed <karahmed@amazon.com>,
        KarimAllah Ahmed <karahmed@amazon.de>,
        kvm list <kvm@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        "the arch/x86 maintainers" <x86@kernel.org>,
        Asit Mallick <asit.k.mallick@intel.com>,
        Arjan Van De Ven <arjan.van.de.ven@intel.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Andi Kleen <ak@linux.intel.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Dan Williams <dan.j.williams@intel.com>,
        Jun Nakajima <jun.nakajima@intel.com>,
        David Woodhouse <dwmw@amazon.co.uk>,
        Greg KH <gregkh@linuxfoundation.org>,
        Andy Lutomirski <luto@kernel.org>,
        Ashok Raj <ashok.raj@intel.com>
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You seem to be making the assumption that there is one L2. What if
there are 100 L2s, and only one has write-access to IA32_SPEC_CTRL? Or
what if there once was such an L2, but it's been gone for months? The
current mechanism penalizes *all* L2s if any L2, ever, has
write-access to IA32_SPEC_CTRL.