linux-kernel - [PATCH 3/4] KVM: nVMX: WARN if PML emulation helper is invoked outside of nested guest

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Message-Id: <20200622215832.22090-4-sean.j.christopherson@intel.com>
Date:   Mon, 22 Jun 2020 14:58:31 -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
Subject: [PATCH 3/4] KVM: nVMX: WARN if PML emulation helper is invoked outside of nested guest

WARN if vmx_write_pml_buffer() is called outside of guest mode instead
of silently ignoring the condition.  The only caller is nested EPT's
ept_update_accessed_dirty_bits(), which should only be reachable when
L2 is active.

Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
---
 arch/x86/kvm/vmx/vmx.c | 45 +++++++++++++++++++++---------------------
 1 file changed, 23 insertions(+), 22 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index a2e7e106cc8f..adf83047bb21 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7507,33 +7507,34 @@ static int vmx_write_pml_buffer(struct kvm_vcpu *vcpu, gpa_t gpa)
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 	gpa_t dst;
 
-	if (is_guest_mode(vcpu)) {
-		WARN_ON_ONCE(vmx->nested.pml_full);
+	if (WARN_ON_ONCE(!is_guest_mode(vcpu)))
+		return 0;
 
-		/*
-		 * Check if PML is enabled for the nested guest.
-		 * Whether eptp bit 6 is set is already checked
-		 * as part of A/D emulation.
-		 */
-		vmcs12 = get_vmcs12(vcpu);
-		if (!nested_cpu_has_pml(vmcs12))
-			return 0;
+	if (WARN_ON_ONCE(vmx->nested.pml_full))
+		return 1;
 
-		if (vmcs12->guest_pml_index >= PML_ENTITY_NUM) {
-			vmx->nested.pml_full = true;
-			return 1;
-		}
+	/*
+	 * Check if PML is enabled for the nested guest. Whether eptp bit 6 is
+	 * set is already checked as part of A/D emulation.
+	 */
+	vmcs12 = get_vmcs12(vcpu);
+	if (!nested_cpu_has_pml(vmcs12))
+		return 0;
 
-		gpa &= ~0xFFFull;
-		dst = vmcs12->pml_address + sizeof(u64) * vmcs12->guest_pml_index;
-
-		if (kvm_write_guest_page(vcpu->kvm, gpa_to_gfn(dst), &gpa,
-					 offset_in_page(dst), sizeof(gpa)))
-			return 0;
-
-		vmcs12->guest_pml_index--;
+	if (vmcs12->guest_pml_index >= PML_ENTITY_NUM) {
+		vmx->nested.pml_full = true;
+		return 1;
 	}
 
+	gpa &= ~0xFFFull;
+	dst = vmcs12->pml_address + sizeof(u64) * vmcs12->guest_pml_index;
+
+	if (kvm_write_guest_page(vcpu->kvm, gpa_to_gfn(dst), &gpa,
+				 offset_in_page(dst), sizeof(gpa)))
+		return 0;
+
+	vmcs12->guest_pml_index--;
+
 	return 0;
 }
 
-- 
2.26.0