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Subject: Re: [PATCH] KVM: nVMX: Use vmx_need_pf_intercept() when deciding if
 L0 wants a #PF
To:     Sean Christopherson <seanjc@google.com>
Cc:     Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, Peter Shier <pshier@google.com>,
        Oliver Upton <oupton@google.com>
References: <20210812045615.3167686-1-seanjc@google.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <6b250262-9ba8-0753-1dd2-0b0d4b5d0186@redhat.com>
Date:   Thu, 12 Aug 2021 18:18:53 +0200
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On 12/08/21 06:56, Sean Christopherson wrote:
> Use vmx_need_pf_intercept() when determining if L0 wants to handle a #PF
> in L2 or if the VM-Exit should be forwarded to L1.  The current logic fails
> to account for the case where #PF is intercepted to handle
> guest.MAXPHYADDR < host.MAXPHYADDR and ends up reflecting all #PFs into
> L1.  At best, L1 will complain and inject the #PF back into L2.  At
> worst, L1 will eat the unexpected fault and cause L2 to hang on infinite
> page faults.
> 
> Note, while the bug was technically introduced by the commit that added
> support for the MAXPHYADDR madness, the shame is all on commit
> a0c134347baf ("KVM: VMX: introduce vmx_need_pf_intercept").
> 
> Fixes: 1dbf5d68af6f ("KVM: VMX: Add guest physical address check in EPT violation and misconfig")
> Cc: stable@vger.kernel.org
> Cc: Peter Shier <pshier@google.com>
> Cc: Oliver Upton <oupton@google.com>
> Cc: Jim Mattson <jmattson@google.com>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>   arch/x86/kvm/vmx/nested.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index bc6327950657..8bcbe57b560f 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -5830,7 +5830,8 @@ static bool nested_vmx_l0_wants_exit(struct kvm_vcpu *vcpu,
>   		if (is_nmi(intr_info))
>   			return true;
>   		else if (is_page_fault(intr_info))
> -			return vcpu->arch.apf.host_apf_flags || !enable_ept;
> +			return vcpu->arch.apf.host_apf_flags ||
> +			       vmx_need_pf_intercept(vcpu);
>   		else if (is_debug(intr_info) &&
>   			 vcpu->guest_debug &
>   			 (KVM_GUESTDBG_SINGLESTEP | KVM_GUESTDBG_USE_HW_BP))
> 

Queued, thanks.

Paolo