linux-kernel - Re: [PATCH 0/2] KVM: x86: Emulate L2 triple fault without killing L1

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Date:   Tue, 2 Mar 2021 18:49:04 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>
Subject: Re: [PATCH 0/2] KVM: x86: Emulate L2 triple fault without killing L1

On 02/03/21 18:45, Sean Christopherson wrote:
> If KVM (L0) intercepts #GP, but L1 does not, then L2 can kill L1 by
> triggering triple fault.  On both VMX and SVM, if the CPU hits a fault
> while vectoring an injected #DF (or I supposed any #DF), any intercept
> from the hypervisor takes priority over triple fault.  #PF is unlikely to
> be intercepted by L0 but not L1.  The bigger problem is #GP, which is
> intercepted on both VMX and SVM if enable_vmware_backdoor=1, and is also
> now intercepted for the lovely VMRUN/VMLOAD/VMSAVE errata.
> 
> Based on kvm/queue, commit fe5f0041c026 ("KVM/SVM: Move vmenter.S exception
> fixups out of line").  x86.c and svm/nested.c conflict with kvm/master.
> They are minor and straighforward, but let me know if you want me to post
> a version based on kvm/master for easier inclusion into 5.12.

I think it would be too intrusive.  Let's stick this in 5.13 only.

Paolo

> Sean Christopherson (2):
>    KVM: x86: Handle triple fault in L2 without killing L1
>    KVM: nSVM: Add helper to synthesize nested VM-Exit without collateral
> 
>   arch/x86/include/asm/kvm_host.h |  1 +
>   arch/x86/kvm/lapic.c            |  2 +-
>   arch/x86/kvm/svm/nested.c       | 57 ++++++++-------------------------
>   arch/x86/kvm/svm/svm.c          |  6 +---
>   arch/x86/kvm/svm/svm.h          |  9 ++++++
>   arch/x86/kvm/vmx/nested.c       |  9 ++++++
>   arch/x86/kvm/x86.c              | 29 +++++++++++++----
>   arch/x86/kvm/x86.h              |  2 ++
>   8 files changed, 60 insertions(+), 55 deletions(-)
>