linux-kernel - [PATCH] KVM: nVMX: Use vmx_need_pf_intercept() when deciding if L0 wants a #PF

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Message-Id: <20210812045615.3167686-1-seanjc@google.com>
Date:   Wed, 11 Aug 2021 21:56:15 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        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, Peter Shier <pshier@...gle.com>,
        Oliver Upton <oupton@...gle.com>
Subject: [PATCH] KVM: nVMX: Use vmx_need_pf_intercept() when deciding if L0
 wants a #PF

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@...r.kernel.org
Cc: Peter Shier <pshier@...gle.com>
Cc: Oliver Upton <oupton@...gle.com>
Cc: Jim Mattson <jmattson@...gle.com>
Signed-off-by: Sean Christopherson <seanjc@...gle.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))
-- 
2.33.0.rc1.237.g0d66db33f3-goog