[v12,77/77] KVM: x86: call the page tracking code on emulation failure

Commit Message

Adalbert Lazăr Oct. 6, 2021, 5:31 p.m. UTC

From: Mihai Donțu <[e-mail]>

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 <[e-mail]>
Signed-off-by: Adalbert Lazăr <[e-mail]>
---
 arch/x86/kvm/x86.c | 49 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 49 insertions(+)

Patch

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 9a3fac9b30ba..a9caacea0207 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7872,6 +7872,51 @@  int x86_decode_emulated_instruction(struct kvm_vcpu *vcpu, int emulation_type,
 }
 EXPORT_SYMBOL_GPL(x86_decode_emulated_instruction);
 
+/*
+ * 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 = static_call(kvm_x86_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, gpa_t cr2_or_gpa,
 			    int emulation_type, void *insn, int insn_len)
 {
@@ -7905,6 +7950,8 @@  int x86_emulate_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
 				kvm_queue_exception(vcpu, UD_VECTOR);
 				return 1;
 			}
+			if (!kvm_page_track_emulation_failure(vcpu, cr2_or_gpa))
+				return 1;
 			if (reexecute_instruction(vcpu, cr2_or_gpa,
 						  write_fault_to_spt,
 						  emulation_type))
@@ -7974,6 +8021,8 @@  int x86_emulate_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
 		return 1;
 
 	if (r == EMULATION_FAILED) {
+		if (!kvm_page_track_emulation_failure(vcpu, cr2_or_gpa))
+			return 1;
 		if (reexecute_instruction(vcpu, cr2_or_gpa, write_fault_to_spt,
 					emulation_type))
 			return 1;