linux-kernel - [PATCH v2 7/7] KVM: nVMX: WARN on attempt to switch the currently loaded VMCS

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Message-Id: <20200923184452.980-8-sean.j.christopherson@intel.com>
Date:   Wed, 23 Sep 2020 11:44:52 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <sean.j.christopherson@...el.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, Dan Cross <dcross@...gle.com>,
        Peter Shier <pshier@...gle.com>
Subject: [PATCH v2 7/7] KVM: nVMX: WARN on attempt to switch the currently loaded VMCS

WARN if KVM attempts to switch to the currently loaded VMCS.  Now that
nested_vmx_free_vcpu() doesn't blindly call vmx_switch_vmcs(), all paths
that lead to vmx_switch_vmcs() are implicitly guarded by guest vs. host
mode, e.g. KVM should never emulate VMX instructions when guest mode is
active, and nested_vmx_vmexit() should never be called when host mode is
active.

Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
---
 arch/x86/kvm/vmx/nested.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 63550dcf6b9f..4bddda078370 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -258,7 +258,7 @@ static void vmx_switch_vmcs(struct kvm_vcpu *vcpu, struct loaded_vmcs *vmcs)
 	struct loaded_vmcs *prev;
 	int cpu;
 
-	if (vmx->loaded_vmcs == vmcs)
+	if (WARN_ON_ONCE(vmx->loaded_vmcs == vmcs))
 		return;
 
 	cpu = get_cpu();
-- 
2.28.0