linux-kernel - Re: [PATCH v8 7/8] KVM: x86: Introduce MSR filtering

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Date:   Mon, 28 Sep 2020 09:09:24 -0700
From:   Aaron Lewis <aaronlewis@...gle.com>
To:     Alexander Graf <graf@...zon.com>
Cc:     kvm list <kvm@...r.kernel.org>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        KarimAllah Raslan <karahmed@...zon.de>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 7/8] KVM: x86: Introduce MSR filtering

On Fri, Sep 25, 2020 at 7:35 AM Alexander Graf <graf@...zon.com> wrote:
>
> It's not desireable to have all MSRs always handled by KVM kernel space. Some
> MSRs would be useful to handle in user space to either emulate behavior (like
> uCode updates) or differentiate whether they are valid based on the CPU model.
>
> To allow user space to specify which MSRs it wants to see handled by KVM,
> this patch introduces a new ioctl to push filter rules with bitmaps into
> KVM. Based on these bitmaps, KVM can then decide whether to reject MSR access.
> With the addition of KVM_CAP_X86_USER_SPACE_MSR it can also deflect the
> denied MSR events to user space to operate on.
>
> If no filter is populated, MSR handling stays identical to before.
>
> Signed-off-by: Alexander Graf <graf@...zon.com>

Reviewed-by: Aaron Lewis <aaronlewis@...gle.com>

>
> ---
>
> v2 -> v3:
>
>   - document flags for KVM_X86_ADD_MSR_ALLOWLIST
>   - generalize exit path, always unlock when returning
>   - s/KVM_CAP_ADD_MSR_ALLOWLIST/KVM_CAP_X86_MSR_ALLOWLIST/g
>   - Add KVM_X86_CLEAR_MSR_ALLOWLIST
>
> v3 -> v4:
>   - lock allow check and clearing
>   - free bitmaps on clear
>