linux-kernel - Re: [PATCH v3 03/37] KVM: nVMX: Invalidate all EPTP contexts when emulating INVEPT for L1

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Message-ID: <CALMp9eR5Uu7nRDOS2nQHGzb+Gi6vjDEk1AmuiqkkGWFjKNG+sA@mail.gmail.com>
Date:   Mon, 23 Mar 2020 09:24:25 -0700
From:   Jim Mattson <jmattson@...gle.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>, kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ben Gardon <bgardon@...gle.com>,
        Junaid Shahid <junaids@...gle.com>,
        Liran Alon <liran.alon@...cle.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        John Haxby <john.haxby@...cle.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Tom Lendacky <thomas.lendacky@....com>
Subject: Re: [PATCH v3 03/37] KVM: nVMX: Invalidate all EPTP contexts when
 emulating INVEPT for L1

On Fri, Mar 20, 2020 at 2:29 PM Sean Christopherson
<sean.j.christopherson@...el.com> wrote:
>
> Free all L2 (guest_mmu) roots when emulating INVEPT for L1.  Outstanding
> changes to the EPT tables managed by L1 need to be recognized, and
> relying on KVM to always flush L2's EPTP context on nested VM-Enter is
> dangerous.
>
> Similar to handle_invpcid(), rely on kvm_mmu_free_roots() to do a remote
> TLB flush if necessary, e.g. if L1 has never entered L2 then there is
> nothing to be done.
>
> Nuking all L2 roots is overkill for the single-context variant, but it's
> the safe and easy bet.  A more precise zap mechanism will be added in
> the future.  Add a TODO to call out that KVM only needs to invalidate
> affected contexts.
>
> Fixes: b119019847fbc ("kvm: nVMX: Remove unnecessary sync_roots from handle_invept")

The bug existed well before the commit indicated in the "Fixes" line.