[RFC PATCH v7 78/78] KVM: x86: call the page tracking code on emulation failure

["Adalbert Lazăr" <alazar@bitdefender.com>]

From: Mihai Donțu <mdontu@bitdefender.com>

The information we can provide this way is incomplete, but current users
of the page tracking code can work with it.

Signed-off-by: Mihai Donțu <mdontu@bitdefender.com>
Signed-off-by: Adalbert Lazăr <alazar@bitdefender.com>
---
 arch/x86/kvm/x86.c | 49 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 49 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index b87ff31ce486..45ba3497484e 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6686,6 +6686,51 @@ static bool is_vmware_backdoor_opcode(struct x86_emulate_ctxt *ctxt)
 	return false;
 }
 
+/*
+ * With introspection enabled, emulation failures translate in events being
+ * missed because the read/write callbacks are not invoked. All we have is
+ * the fetch event (kvm_page_track_preexec). Below we use the EPT/NPT VMEXIT
+ * information to generate the events, but without providing accurate
+ * data and size (the emulator would have computed those). If an instruction
+ * would happen to read and write in the same page, the second event will
+ * initially be missed and we rely on the page tracking mechanism to bring
+ * us back here to send it.
+ */
+static bool kvm_page_track_emulation_failure(struct kvm_vcpu *vcpu, gpa_t gpa)
+{
+	u64 error_code = vcpu->arch.error_code;
+	u8 data = 0;
+	gva_t gva;
+	bool ret;
+
+	/* MMIO emulation failures should be treated the normal way */
+	if (unlikely(error_code & PFERR_RSVD_MASK))
+		return true;
+
+	/* EPT/NTP must be enabled */
+	if (unlikely(!vcpu->arch.mmu->direct_map))
+		return true;
+
+	/*
+	 * The A/D bit emulation should make this test unneeded, but just
+	 * in case
+	 */
+	if (unlikely((error_code & PFERR_NESTED_GUEST_PAGE) ==
+		     PFERR_NESTED_GUEST_PAGE))
+		return true;
+
+	gva = kvm_x86_ops->fault_gla(vcpu);
+
+	if (error_code & PFERR_WRITE_MASK)
+		ret = kvm_page_track_prewrite(vcpu, gpa, gva, &data, 0);
+	else if (error_code & PFERR_USER_MASK)
+		ret = kvm_page_track_preread(vcpu, gpa, gva, 0);
+	else
+		ret = true;
+
+	return ret;
+}
+
 int x86_emulate_instruction(struct kvm_vcpu *vcpu,
 			    unsigned long cr2,
 			    int emulation_type,
@@ -6738,6 +6783,8 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu,
 				kvm_queue_exception(vcpu, UD_VECTOR);
 				return 1;
 			}
+			if (!kvm_page_track_emulation_failure(vcpu, cr2))
+				return 1;
 			if (reexecute_instruction(vcpu, cr2, write_fault_to_spt,
 						emulation_type))
 				return 1;
@@ -6795,6 +6842,8 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu,
 		return 1;
 
 	if (r == EMULATION_FAILED) {
+		if (!kvm_page_track_emulation_failure(vcpu, cr2))
+			return 1;
 		if (reexecute_instruction(vcpu, cr2, write_fault_to_spt,
 					emulation_type))
 			return 1;